Investigation of the Global Escarpment, including the Fretted Terrain,
in the Martian Northern Hemisphere
by
Benjamin Chad Harrold
A thesis submitted to the Graduate Faculty of
Auburn University
in partial fulfillment of the
requirements for the Degree of
Master of Science
Auburn, Alabama
August 9, 2010
Copyright 2010 by Benjamin Chad Harrold
Approved by
David T. King Jr., Co-Chair, Professor of Geology
Luke J. Marzen, Co-Chair, Associate Professor of Geography
Lorraine W. Wolf, Professor of Geology
Abstract
The global escarpment and associated fretted terrain are located in the Martian
northern hemisphere. Two competing hypothesis presently in play explain the origin of
Mars? global escarpment. These hypotheses involve endogenic and exogenic processes
and both could help explain the extreme topographic difference between the southern
highlands and the northern lowlands. The focus of this study, the fretted terrain area of
the global escarpment, is a transition zone of mesa-like features located directly north of
the global escarpment. With the use of digital imagery analysis, georeferencing of
existing maps, and the interpretation of current models, the most plausible origin of the
escarpment proposed herein would be an exogenic process, namely a single, mega-scale
impact shortly after formation of the planet. The main lines of evidence supporting this
favored hypothesis are the modeled elliptical shaped basin, similarities between crustal
thickness and topographic elevations, mineralogy, and the orientation and size
distribution of the northern fretted terrain.
ii
Acknowledgments
The author would like to thank the members of his thesis committee, Drs. David
King, Luke Marzen, and Lorraine Wolf for their unequivocal support and guidance
during this project. The author is particularly grateful to Dr. King for ?originally
suggesting this line of inquiry.? The author is also grateful to Dr. Marzen, whose grant
proposal and expertise in GIS helped initiate this project.
The author acknowledges the extensive use of multiple publicly accessible
imagery databases including Arizona State University ,
NASA , Planetary Data
System (PDS) , U.S.G.S Planetary GIS Web Server
http://webgis.wr.usgs.gov/pigwad/maps/index.html, http://www.ian-ko.com/ ET
GeoTools for ArcGIS and Google Earth 5.0.
The author would like to dedicate this thesis to his family and friends for their
moral and intellectual support over these past two years: ?Pops and Mammy, thanks for
instilling me with the courage, intelligence, wisdom, and strength to pursue any dream in
life. Josh, thank you for always putting a smile on my face and teaching me to be a better
sibling. Bart, thanks for the endless quest for patience with computer software. And
finally, to my wife Joy, who replanted the seed of discovery and taught me what love,
compassion, and unselfishness are all about.?
iii
Table of Contents
Abstract............................................................................................................................... ii
Acknowledgments ............................................................................................................. iii
List of Tables ..................................................................................................................... vi
List of Figures................................................................................................................... vii
Introduction ........................................................................................................................1
Objectives and Significance of Study..................................................................................5
Geologic History of Mars ..................................................................................................6
Physical..................................................................................................................10
Chemical ................................................................................................................14
Bulk Composition ..............................................................................................................17
The Core ...............................................................................................................20
The Mantle.............................................................................................................21
The Crust and Soil .................................................................................................23
The Global Escarpment ....................................................................................................26
Endogenic Processes..............................................................................................26
Exogenic Processes................................................................................................27
The Fretted Terrain ............................................................................................................35
Missions and Instrumentation............................................................................................40
Mars Global Surveyor............................................................................................40
iv
Mars Reconnaissance Orbiter ................................................................................42
Mars Odyssey.........................................................................................................43
Methodology......................................................................................................................46
Data Extraction ......................................................................................................46
Data Incorporation .................................................................................................49
Analysis Techniques ..............................................................................................52
Results................................................................................................................................57
Regional Analysis ..................................................................................................57
Sectional Analysis..................................................................................................71
Local Analysis .......................................................................................................76
Interpretation and Discussion ............................................................................................81
Endogenic Processes..............................................................................................82
Exogenic Processes................................................................................................90
The Fretted Terrain ................................................................................................98
Conclusion and Further Work..........................................................................................116
References........................................................................................................................118
Appendix .......................................................................................................................127
GIS Applications..................................................................................................127
List of Images ......................................................................................................130
v
List of Tables
Table 1. Calculated bulk composition for Mars using three different sources. Modified
from Boyce (2002) ............................................................................................................19
Table 2. Analysis of weight % of five rocks from the Pathfinder Lander Site. From
Cattermole (2001) .............................................................................................................24
Table 3. Chemical composition in weight % of six soils from Pathfinder Landing Site.
From Cattermole (2001) ...................................................................................................25
Table 4. List of largest known impact basins in the Solar system. From USGS 2010a
Planetary Nomenclature. (Accessed on 12 Jan., 2010) .....................................................30
Table 5. Analysis of fretted terrain composed in ArcGIS 9.2 ..........................................72
vi
List of Figures
Figure 1. Outlined study area of the global escarpment of Mars. Each quadrangle is 30 x
30 degrees. Modified from http://webgis.wr.usgs.gov/website/mars_html/viewer.htm
including the current USGS PIGWAD map, MOLA layer. (Accessed 14 Oct., 2008).......2
Figure 2. Example of the fretted terrain found in the northern hemisphere on the global
escarpment. From http://webgis.wr.usgs.gov/website/mars_html/viewer.htm including the
current USGS PIGWAD map, Themis layer. Themis image V11918012 located in red
box. (Accessed 14 Oct., 2008).............................................................................................4
Figure 3. Generalized geologic map of Mars showing the distribution of major material
types as described in the text. Unit age abbreviation: N, Noachian; H, Hesperian; A,
Amazonian; E, Early; L, Late .This is a Mollweide projection, centered on 260?E. Data
are from Mars Orbiter Laser Altimeter (MOLA) using shaded relief on Mars, 1? latitude
= 59 km. Adapted from Scott et al. (1986-1987) and Tanaka (2003)..................................7
Figure 4. Geologic Map of Mars derived by crater density ratios. From Scott and Carr
(1978)...................................................................................................................................9
Figure 5. Geologic time scales of Mars using crater density and mineralogy. Modified
from Gangale (2007)..........................................................................................................10
Figure 6. Artistic rendition of a possible wet Mars from the past. From
http://svs.gsfc.nasa.gov/vis/a000000/a002200/a002291/index.html (Accessed on 7 Feb.,
2010; NASA 2010c /Goddard Space Flight Center Scientific Visualization Studio). ......15
Figure 7. Diagram composed of several meteorites along with multiple orbital and lander
missions assessing the Martian regolith. From Bell (2008)...............................................20
Figure 8. Example of degree-1 mantle convection plume model. From Roberts and
Zhong (2006) .....................................................................................................................27
vii
Figure 9. Views of the Borealis Basin: (a) polar projection around the basin center at
67? N, 208? E, showing the present-day topography and shaded relief of Mars; (b) the
modeled crustal root; (c) the topographic gradient at 4? wavelength; (d) traced dichotomy
boundary is shown and compared with the best-fit ellipse (southern boundary of Arabia
Terra denoted by dashed line); (e) outlines of the northern and southern edges of Arabia
Terra (dotted lines; approximated using a threshold crustal thickness) are shown over a
crustal thickness map with the reconstructed basin rim required to restore the crustal
thickness in Arabia Terra to the mean highlands value; (f) reconstructed crustal thickness
before basin modification in Arabia Terra. From Andrews-Hanna et al. (2008) ..............29
Figure 10. Cylindrical projections of: (a) topography
(MOLA data) and (b) crustal
thickness
from Neumann et al. (2008) of Mars. Main features labeled in a include Tharsis
(Th), Arabia Terra (AT), Hellas (H), Argyre (A), and Utopia (U), as well as the Borealis
basin outline proposed by Wilhelms and Squyres (1984). In these cylindrical projections,
crustal thickness was modeled with perturbation (isostatic root) showing continuation of
the dichotomy boundary beneath Tharsis; (c) The observed dichotomy boundary (thin
line) is compared with the best-fit ellipse (bold line). The break in slope separating
Arabia Terra from the highlands is shown as a dashed line. From Andrews-Hanna et al.
(2008).................................................................................................................................33
Figure 11. Map showing the location of the fretted terrain used in this project. Modified
from USGS MOLA DEM (1999) ......................................................................................35
Figure 12. Example of terrace formation due to a large meteor impact at zero on the
horizontal scale. From Morgan et al. (2000)......................................................................36
Figure 13. Image of terrestrial, small scale, ice-wedge polygons located in Barrow,
Alaska. From Lucchitta (1980)..........................................................................................37
Figure 14. Mars northern polar view: (a) Lambert equal area projection of MOLA
Northern Pole-to-equator topography from Smith et al. (1999). Black lines indicate
positions of contacts interpreted to be shorelines; (b) Major features as seen in (a). From
Head et al. (1999)...............................................................................................................38
Figure 15. Satellites that generated data used in this project: (a) Mars Global Surveyor;
(b) Mars Reconnaissance Orbiter; (c) Mars Odyssey Spacecraft. All images from NASA
2010d. (Available from http://mars.jpl.nasa.gov/gallery/spacecraft/index.html) ..............45
Figure 16. Applications in imagery overlays in Google Earth 5.0 ....................................48
Figure 17. MDMI 2.1 and visible map with image overlays from context camera in
Google Earth 5.0 ................................................................................................................50
Figure 18. Defining projection of MOLA digital elevation model in ArcMap 9.2 ...........51
viii
Figure 19. Geoprocessing of MOLA data for extraction of fretted terrain........................56
Figure 20. (a) Geologic Map of Mars including the northern escarpment; (b) Geologic
Map of Mars including the southern escarpment; (c) Modeled crustal thickness map (0.5
pixel/degree), (White line delineates escarpment boundary line). Image modified from
Scott and Carr (1978); Andrews- Hanna et al. (2008)................................................. 59-61
Figure 21. Cross sections along the entire global escarpment: (a) Two regional cross
sections of the northern low global escarpment; (b) Two regional cross sections of the
northern global escarpment; (c) Two regional cross sections of the southern global
escarpment (scale = meters)...............................................................................................63
Figure 22. Intensity value map derived from TES mineralogical data: (a) basalt; (b)
andesite (4pixel/degree. White line delineates global escarpment). Images from Arizona
State University, Mars Global Data Sets (2006)................................................................65
Figure 23. (1a-d) Bowen?s discontinuous reaction series including quartz acquired from
TES mineralogical data: (1a) olivine; (1b) clinopyroxene; (1c) amphibole; (1d) quartz.
(2a-d) Bowen?s continuous reaction series including hematite acquired from TES
mineralogical data: (2a) plagioclase; (2b) feldspar; (2c) orthoclase; (2d) hematite. Images
from Arizona State University, Mars Global Data Sets (2006)................................... 67-70
Figure 24. 24. Chart showing size distribution on both classes of fretted terrain (Data
from table 5).......................................................................................................................73
Figure 25. Mosaic of CTX images composed in Google Earth 5.0: (a) examples of
northern fretted blocks < 50 km from escarpment; (b) examples of northern low fretted
blocks > 200 km from escarpment. Images from Arizona State University, Context
Camera Images (2007 ? 2008)...........................................................................................74
Figure 26. Sinuous nature of fluid transport along the northern global escarpment.
Modified from USGS MOLA DEM (1999); north fretted terrain ? beige blocks; red
arrows ? areas of fluid incision..........................................................................................75
Figure 27. CRISM image 0000AC07 from Google Earth 5.0 showing varied mineralogy
found in the fretted valley regions. Images from Arizona State University, CRISM
Images 2008.......................................................................................................................76
Figure 28. CRISM images 0008986 and 0009605 showing mass wasting/ gravity driven
processes along the margins of the fretted blocks. Images from NASA 2010e Planetary
Data Systems (PDS; 2006).................................................................................................78
Figure 29. Example of HiRISE images showing lineated valley fill found between fretted
blocks. HiRISE image 005737 from Arizona State University 2007 ................................80
ix
Figure 30. One possible view of the Martian interior. From Stevenson (2001) ................83
Figure 31. Example of Rayleigh-Taylor instability analysis with 3 differing viscosities.
Radius to initial boundary is 1325 km with an 80 km thick lid. From Zhong and Zuber
(2001).................................................................................................................................85
Figure 32. Modeled crustal thickness map (0.5 pixel/degree, White line delineates
escarpment boundary line). Image modified from Andrews- Hanna et al. (2008)............86
Figure 33. Picture depicting sea floor spreading through time A-D, which produces a
steep terrace. From Scienceray 2010, Great discoveries in the field of Earth science.
(Accessed: 24 May 2010). .................................................................................................89
Figure 34. Topographic and Crustal thickness maps: (a) MOLA relief map, Black line is
traced escarpment; (b) crustal thickness map, Black line is traced escarpment; ellipses
mark sites of major thinning due to impacts. Images were modified from USGS MOLA
DEM (1999) and Andrews- Hanna (2008). .......................................................................92
Figure 35. Comparison of three major elliptical basins: (a) north polar projection of
Martian topography; (b) modeled crustal thickness of Mars removing the Tharsis rise; (c)
topographic polar projection of the South-Pole Aitken basin on the Moon; (d) the Hellas
basin on Mars. Modified from Google Earth 5.0, USGS MOLA DEM (1999), and
Andrews-Hanna et al. (2008).............................................................................................94
Figure 36. MOLA greyscale DEM: (a) northern escarpment - light blue line, 50 km
buffers - red and blue lines, fretted terrain - green polygons; and (b) northern low
escarpment - yellow line, 50 km buffers - red and blue dashed line, northern low fretted
terrain - yellow polygons. Modified from USGS MOLA DEM (1999)............................96
Figure 37. Possible motion of lithosphere and underlying fluidized mantle material during
a major impact. From Melosh (1989) ................................................................................97
Figure 38. MOLA greyscale DEM showing two regions of escarpment and fretted terrain
(blue line - northern escarpment, green polygons - northern fretted terrain, yellow line -
northern low escarpment, yellow polygons - northern low fretted terrain). Modified from
USGS MOLA DEM (1999)...............................................................................................99
Figure 39. Possible cohesive, rafted fretted blocks of same elevation located at least 150
km from the global escarpment. Black line ? global escarpment; beige blocks ? northern
fretted terrain blocks; red dashed circles ? possible rafted blocks. Modified from USGS
MOLA DEM (1999). .......................................................................................................100
x
Figure 40. Orientation and elevation of the fretted terrain: (a) orientation of fretted blocks
with center of mass, long, and short axes; (b) reclassification of MOLA DEM showing
consistent elevations. Modified from USGS MOLA DEM (1999) .................................101
Figure 41. Sections of the global escarpment composed from MOLA-based DEM: (a)
northern section (black line - northern global escarpment, red polygons - northern fretted
blocks, black dots - center of mass of polygon, and white lines- long and short axis); (b)
northern low section (black line - northern low escarpment, white polygons - northern
low fretted blocks, red circles - post escarpment formation impact sites). Modified from
USGS MOLA DEM (1999).............................................................................................102
Figure 42. (a) Reclassified MOLA-based DEM of proposed ancient high stand shore
lines: northern low escarpment area (black dashed line - northern low escarpment, red
polygons - northern low fretted blocks); (b) Reclassified MOLA-based DEM of proposed
ancient high stand shore lines: northern escarpment area (dashed red line - northern
escarpment; Northern polygons are outlined in black). Modified from USGS MOLA
DEM (1999)............................................................................................................. 104-105
Figure 43. (a) Reclassified MOLA-based DEM of proposed ancient high stand shore
lines: northern low escarpment area (black dashed line - northern low escarpment, red
polygons - northern low fretted blocks); (b) Reclassified MOLA-based DEM of proposed
ancient high stand shore lines: northern escarpment area (dashed red line - northern
escarpment; Northern polygons are outlined in black). Modified from USGS MOLA
DEM (1999).....................................................................................................................107
Figure 44. Insolation, eccentricity, and obliquity of Martian polar region over two time
scales. From Lasker (2002)..............................................................................................109
Figure 45. Movement of ices on the Martian surface through time. Modified from
Sch?rghofer (2007). .........................................................................................................111
Figure 46. Possible glacial activity on the Martian surface: (a) Wide field view of CTX
image P01_001570_2213_XI_41N305W in Google Earth with possible ice induced
movement highlighted in red circles; (b) Overhead close up view of the same CTX image
in Google Earth with possible end moraines at margin of a fretted block; (c) Cirque-like
feature with end moraines viewed at 60?from horizontal in Google Earth. Vertical
exaggeration 3:1. Images from Arizona State University, Context images 2006.... 112-114
Figure 47. HiRISE image PSP_005738_2245RED showing possible cryogenic karst
alteration found in the northern low fretted terrain. Image from Arizona State University,
HiRISE database (2007) ..................................................................................................115
xi
1
INTRODUCTION
The geomorphic evolution of the Martian surface has been an ongoing process
since the planet?s formation about 4.6 billion years ago. These changes are apparent when
the topography is examined. Mars has many striking surface features including some of
the highest peaks (e.g., Olympus Mons) and deepest canyons (e.g., Valles Marineris) in
the solar system. Another less studied but equally significant feature is the global
escarpment located in the northern hemisphere (Fig. 1).
2
Figure
1. Outli
ne
d st
udy a
rea
of the
global e
sca
rpment of
Mar
s. Ea
ch qua
dra
ngle is 30 x 30 de
gre
es.
Modi
fie
d fr
om
htt
p:/
/we
bgis.wr.usgs.gov/we
bsit
e/m
ars_html
/vi
ewe
r.htm
including t
he
cu
rre
nt US
GS P
IG
W
AD
m
ap, MOLA
laye
r.
(Ac
cessed
14 O
ct., 2008)
.
3
The boundary between the highlands of the southern hemisphere and the lowlands
of the northern hemisphere, sometimes referred to as the Martian dichotomy, is marked
with elevation changes of up to 1 km in some areas along the global escarpment (Kiefer
2008). The ages of these two regions, south highlands ~4.2 ? 0.8 b.y. and the northern
lowlands ~4.12 ? 0.08 b.y., have been estimated by crater density and comparisons to
other celestial bodies like the Earth?s moon (Tanaka 1986). The approximate age for the
global escarpment?s formation using these techniques is 4.1 to 3.9 b.y. (Watters 2007).
Past studies have revolved around two major theories for the possible formation
of the escarpment: (1) endogenic or internal processes such as mantle convection or plate
tectonics (McGill and Squyres 1991); and (2) exogenic or external processes, such as
large multiple impacts or a single mega-impact (Wilhelms and Squyres 1984). Both
models have strengths and weaknesses and have evolved over the past 30 years with the
addition of new information from satellite remote sensing and improvements in
technology.
The fretted terrain (Fig. 2) is one of several transitional terrains that can be
identified on the Martian surface and is located between the southern highlands and the
northern lowlands. The fretted terrain is thought to have a nearly uniform height clustered
around 0? elevation with respect to the aeriod comprised of polygon-shaped blocks. It is
bounded by an abrupt escarpment in the highlands to the south and transitions into the
knobby terrain to the north (Sharp 1973). The initial formation and evolutionary
processes of this terrain are poorly understood to present date (Irwin and Watters 2004).
4
Figure
2. Exa
mpl
e of t
he
fr
ett
ed ter
rain found in t
he
northe
rn
he
mi
spher
e on
the globa
l esc
arpme
nt. F
rom
htt
p:/
/we
bgis.wr.usgs.gov/we
bsit
e/m
ars_html
/vi
ewe
r.htm
including t
he
cu
rre
nt US
GS P
IG
W
AD
m
ap, The
mi
s
laye
r. The
mi
s im
age
V11
918012 loca
ted in r
ed bo
x. (A
cce
ssed
14 O
ct., 200
8).
5
OBJECTIVES AND SIGNIFICANCE OF STUDY
The objectives of this study are as follows: (1) use new planetary imagery and
data products to review existing theories and propose new hypothesis about the formation
and evolution of the global escarpment, with emphasis on the fretted terrain; and (2) to
integrate findings of this study with existing theories of escarpment and thus provide a
better understanding of the origin and evolution of the fretted terrain.
The current efforts at planetary exploration have gained momentum over the past
two decades with the addition of new technology and a heightened interest in the
scientific community. With publicly accessible imagery and data sets, exploration of
Mars is now more readily achievable than ever before. The origin of the global
escarpment has many interpretations ranging from exogenic models involving a single
impact (Marinova et al. 2008) to multiple impact basins (Frey 1988) to endogenic or
internally driven forces, such as mantle convection (McGill and Dimitriou 1990) or plate
tectonics (Sleep 1994). The information obtained throughout this project is expected to
shed some light in the direction of one or more of these possibilities. Extensively detailed
topographic mapping incorporating all of these imagery layers, aspects, and comparisons
to past projects has yet to be done on this single geomorphic feature of Mars.
6
GEOLOGIC HISTORY OF MARS: PHYSICAL AND CHEMICAL
The geologic history of Mars encompasses many violent and chaotic changes
throughout its nearly 4.6 billion year life span. Because Mars has been physically and
chemically active through time, we can use two types of geomorphic alterations to date
surface features on the planet. These two different methods can be used to delineate two
separate Martian geologic time scales.
The first and oldest method used to physically date the Martian surface is the
impact crater size-frequency method (Nimmo and Tanaka 2005). Using the principles of
superposition and the standard Martian crater counting method, Mars has been divided
into three major epochs (Fig. 3). The cratering rate of Mars has been estimated primarily
by lunar comparisons, which was adjusted for the population of Mars-crossing asteroids
(Hartmann and Neukum 2001). A few issues must be considered while using the Martian
crater count method.
7
Figure
3.
Ge
ne
rali
zed
ge
ologi
c map
of
Mar
s showing
the
dist
ributi
on
of
major
mate
ria
l types
as
de
scribe
d
in
the
text.
Uni
t a
ge
abbre
viation:
N,
Noa
chian;
H,
He
sper
ian;
A,
Ama
zoni
an;
E,
Ea
rly;
L,
La
te
.Th
is
is
a
Mol
lwe
ide
pr
ojec
tion,
center
ed
on
260?E
. D
ata
are
fr
om
Ma
rs
Or
bit
er
La
ser
Alti
me
ter
(MO
LA
) using
shade
d re
lie
f on Mar
s, 1?
latit
ude
= 59 km. Ada
pte
d fr
om S
cott
et al. (
1986
-1987)
and Ta
na
ka
(2003
).
8
First is the total crater density, which is measured by statistically fitting the crater
count data including size distribution to known size frequency functions over varying
ranges of crater diameters (Hartmann and Neukum 2001). The use of large diameter
craters means that large areas must also be covered, which could visually constrain the
limit of smaller geologic units. Lastly, the crater retention age, or the average time
interval for which a specified size crater will be preserved on the surface are biased
toward the younger end of the newly classified geologic unit. These factors can then be
incorporated to give an overall uncertainty factor of 1.2 to 1.3, and suggest a percent error
between 5 to 20% (Hartmann et al. 1981). Because Mars is nearly 4.6 billion years old,
ages derived for the crater counting technique could vary by 200 million to 1 billion
years. Still these crater-density ratios provide relative ages for subdividing Mars into
specific geologic units and enables comparison of differing geomorphic processes
throughout Martian history. Using these techniques, a geologic map was produced by
David Scott and Michael Carr in 1978 (Fig. 4). This map encompasses 24 Martian-rock
stratigraphic units subdivided into five general categories: (1) plains material; (2)
constructional volcanic material; (3) channel and canyon material; (4) rough terrain
material; and (5) polar material.
9
Figure
4. Ge
ologi
c Map
of
Mar
s de
rive
d by
cra
ter
de
nsit
y ra
tios. F
rom
Sc
ott
and Car
r (
1978)
.
10
The three major eras of Martian geologic physical history using the crater size-
frequency method are the Noachian Epoch (4.6 to 3.5 b.y.), the Hesperian Epoch (3.5 to
1.8 b.y.), and the Amazonian Epoch (1.8 b.y. to the present). These names are taken from
the corresponding geographic regions of Mars.
Another more recent time scale which involves the surface mineralogy has been
proposed based on new data from OMEGA Visible and Infrared Mineralogical Mapping
Spectrometer on board the Mars Express Orbiter. Using spectral analysis of Martian
mineralogy, Mars? history is divided into 3 different major epochs. These are the
Phyllocian Epoch (4.6 to 4.0 b.y.), the Theiikian Epoch (4.0 to 3.5 b.y.), and the
Siderikan Epoch (3.5 b.y. to the present (Gangle 2007); Fig. 5). This series divides the
Noachian into two epochs depending on water availability and chemical alterations of the
corresponding surface minerals that were present at that time.
Figure 5. Geologic time scales of Mars using crater density and mineralogy. Modified
from Gangale (2007).
Physical History: The Noachian Epoch (4.5 to 3.5 b.y.)
The first epoch of Martian history, sometimes referred to as the heavy
bombardment era, is the Noachian. This name comes from the Noachis quadrangle where
the oldest rocks on the planet are exposed (Scott and Carr 1978). The Noachian began
with the initial formation of the planet from the proto-planetary disk. As Mars grew in
11
size, it was bombarded with planetesimals. The continued impacts from these asteroid-
like bodies caused some surface regions of Mars to become heated or partially melted
(Lenardic et al. 2004). Planetary heating was enhanced further by radiogenic heat
produced internally.
Crust formation predates the end of the heavy bombardment era. Rock units from
this epoch represent highly brecciated and faulted crustal rocks, evidence of which can be
seen in many large multi-ring basins such as Hellas and Argyre (Scott and Carr 1978).
The surface continued to be bombarded by the remnants of planetary material available,
which caused a great deal of heating near the surface of Mars. A period of wide spread
lava flooding is represented by the extensive tracts of plains between these two ancient
craters (Christiansen 1995). These voluminous flood basalts were extruded from fissures,
but were relatively thin (Scott and Carr 1978). Due to the constant bombardment, these
lava plains and impact ejecta comprise an overlapping and interbedded geologic unit
known as the cratered plateau material (Scott and Carr 1978). This planet wide heating
event which entailed the release of large amounts of volatiles from volcanic edifices was
accompanied by planetary hydrothermal activity or circulation of water possibly melting
large amounts of permafrost that was present in the ground (Baker 2001). The early
Martian atmosphere was likely more dense and atmospheric temperatures were likely
higher. In view of these conditions, potential rainfall and flooding would have caused
sufficient erosion and sediment transportation for large quantities of sediment to have
accumulated in highland basins as well as the northern lowlands (Christiansen 1995).
12
Physical History: The Hesperian Epoch (3.5 to 1.8 b.y.)
The Hesperian is named for the Hesperia Planum in the Mare Tyrrhenum
quadrangle and is split into three rock units: (1) rolling ridge material; (2) ridge plain
material; and (3) streaked plain material (Scott and Carr 1978). The second epoch in
Martian history began at the end of the heavy bombardment and was marked by the
formation of extensive interlayered lava plains and eolian deposits. Later during this
epoch, there was a period of heating and volcanic activity, caused by a hot plume of
material that continued to rise from deep within the interior of Mars toward the Tharsis
Bulge located in the northern hemisphere (McGovern et al. 2002). The crust was then
deformed by the extensional pull from this magma and created the Tharsis Montes,
Olympus Mons, and the other volcanoes accompanied with radial fracturing (McGovern
et al. 2002). The northern hemisphere may have been extensively fractured during this
era due to its thinner crust. The volcanoes and fissures spread lava over the lowlands of
Mars and created a new surface, which shows less meteorite bombardment than do the
older highlands (Frey 2006). Valles Marineris began to develop along this fracture
system, followed by intense runoff evident from the channels produced from the
highlands to lowlands (Tseung and Soare 2006). These were the first wide spread
flooding events to take place on the Martian surface due to melting of ground ice by
volcanism, meteor impacts, or climate change. At this time, the northern plains were
resurfaced by sedimentation (Phillips et al. 2001). Later, the surface temperatures began
to lower as Mars quickly cooled due to its relative size. Atmospheric pressure dropped
due to erosional processes associated with constant solar bombardment, then making it
unlikely for water to continue to exist on the surface. Consequently, water became
13
trapped as permafrost in the Martian soil and volcanism again caused huge amounts to
melt and flood the low-lying areas. Much of the erosion that occurred along the global
escarpment is attributed to this process (Christiansen 1995). At the end of the epoch,
Elysium began to erupt along with highland volcanic centers and the creation of the
Tharsis volcanoes began to develop (Scott and Carr 1978).
Physical History: The Amazonian Epoch (1.8 b.y. to present)
The Amazonian, named for the Amazonis quadrangle is Mars? final epoch and
extends to the present day (Scott and Carr 1978). Ground surfaces of Amazonian age
have a few meteorite impact craters, but otherwise are quite varied constituting volcanic
material, alluvium, and eolian deposits. The Amazonian Epoch has seen localized lava
flows around the huge volcano Olympus Mons and other volcanoes increase in size.
Elsewhere on Mars, landslides formed along the rim of Valles Marineris and along the
global escarpment with continued sediment transportation (Baratoux et al. 2002).
Catastrophic outbreaks of ground water due to the Tharsis rise produced floods and
formed the Chaotic terrain, which are located at the eastern end of Valles Marineris.
These flood events transported sediment to the northern basin and produced short-lived
seas. The Chaotic terrain was enlarged and the Global escarpment continued its southerly
retreat (Christiansen 1995). Eolian processes continued to change the surface of the
planet to the present day smoothing the overall appearance of Mars. The thickness of
these deposits varies greatly ranging from thin sheets to thick accumulations that
sometimes bury craters to depths of a few kilometers (Scott and Carr 1978).
14
Chemical History: The Phyllocian Epoch (4.6 to 4.0 b.y.)
The first chemical/alternative Epoch of Martian history is the Phyllocian. This
epoch receives it name for the abundance of phyllosilicates that were formed during the
first 500 million years of Martian existence. These clay-rich minerals, which include Fe-
rich (chamosite and nontronite) and Al-rich (montmorillonite), require an alkaline-rich
water environment in which to form (Bibring et al. 2006). These conditions would not
require high temperatures and would indicate extensively wet periods with alkaline
waters resulting from chemical alteration. Thus, we can deduce that - during this epoch -
Mars must have had liquid water present at or near the surface early in its evolutionary
process (Fig. 6). Clay minerals may have also been formed in the subsurface by three
processes: (1) hydrothermal activity; (2) cratering, that supplied subsurface water to the
impacted material; or (3) mantle cooling (Bibring et al. 2006).
15
Figure 6. Artistic rendition of a possible wet Mars from the past. From
http://svs.gsfc.nasa.gov/vis/a000000/a002200/a002291/index.html (Accessed on 7 Feb.,
2010; NASA 2010c /Goddard Space Flight Center Scientific Visualization Studio).
Chemical History: The Theiikian Epoch (4.0 to 3.5 b.y.)
The Theiikian Epoch is dominated by the presence of sulfate minerals. Because
Mars was extremely active volcanically during this period, huge quantities of sulfur
dioxide along with other volatiles were expelled into the atmosphere. These volatiles
precipitated and then mixed with surface waters that were either still present or part of a
replenishment process on the Martian surface. Sulfate mineral formation requires
considerable amounts of water to be present and then evaporate confining it to a surface
process (Bibring et al. 2006).
16
Chemical History: The Siderikian Epoch (3.5 b.y. to present)
The final alternative epoch is the first one in which water does not play any
sustainable role. This can be found in the lack of hydration of the ferric oxides in
comparison to hydrated phyllosilicates and sulfates. The atmosphere and water have
disappeared along with a waning of volcanism and global cooling. Ferric oxides formed
as an alteration product resulting from atmospheric weathering through peroxide
reactivity (Bibring et al. 2006).
17
BULK COMPOSITION OF MARS
The knowledge of the bulk properties of a planet can lend us invaluable
information about the interior of a planet. These properties include mass, size, density,
composition, and moment of inertia. If we begin by using the mass, size, and shape of the
planet, we are able to calculate the bulk density and moment of inertia. The bulk
composition can be estimated from the bulk density and using the moment of inertia we
can determine if that planet were able to differentiate into layers (Bertka and Fei 1998).
Since 1997, when the Mars Global Survey arrived at Mars, researchers have used one of
its five instruments (Mars Orbital Laser Altimeter) to gain accurate measurements (~460
m horizontally and ~1 m vertically) of the topography. Using these data, an equatorial
diameter of 6,792.19 km and a polar diameter of 6,752.4 km have been determined and in
addition a mass of 6.44 x 1023 kg and total bulk density of 3.906 g/cm3 have been
computed (Cattermole 2001). This mass can also be calculated by the gravitational
interaction between Mars and the orbital paths of Phobos and Deimos and also by Mars?
effect on past satellite flybys and more recent orbiters. In comparison to the other
terrestrial planets, Mercury (5.44 g/cm3), Venus (5.25 g/cm3), and Earth (5.52 g/cm3), this
bulk density is relatively low. The lower density can be attributed to the initial conditions
during formation of the planet. Specifically, the nebular condensation model would
predict that light volatiles like water would be sufficiently incorporated farther from the
sun (Christiansen 1995). Early in the planetary accretion process, metallic iron mixed
18
with primordial water producing iron oxides via chemical reactions, which were
incorporated into the interior of Mars. The other terrestrial planets with higher mean
densities located closer to the sun did not readily blend the iron and water; hence they
have appreciably less iron oxide that Mars (Boyce 2002).With the data acquired from the
mass, size, and shape, we can now calculate the moment of inertia. This indicates
whether a planet has separated into layers, and for Mars we find that it is similar to Earth
i.e., it possesses a core, mantle, and crust. Even though the presence of layers can be
determined through this process, unfortunately a thickness for each layer cannot. The
composition of a planet is also a useful property and can be obtained from rock samples.
Presently, we have samples of Martian rocks in the form of meteorites. These SNC
meteorites (named after the three types of igneous meteorites-shergottites, nakhlites, and
chassigny) are pieces of the Martian crust blasted off the surface by large impactors
(Table 1). Pockets of gases trapped in the glasses within these meteorites are chemically
consistent with what we know of Mars? atmosphere. For example, gases analyzed from
the shergottite meteorite chemically and isotopically match those currently found in the
Martian atmosphere lending evidence that they indeed came from the red planet (Bogard
et al. 1984).
19
Table 1. Calculated bulk composition for Mars using three different sources. Modified
from Boyce (2002).
Constituents
Composition
Similar to
Chondritic
Meteorites (%)
Composition
Calculated from
SNC Composition
(%)
Terrestrial
Mantle and
Crust (%)
Mantle and Crust
SiO? 41.6 44.4 45.1
TiO? 0.3 0.1 0.2
Al?O? 6.4 3 4
Cr?O? 0.6 0.8 0.5
MgO 29.8 30.2 38.3
FeO 15.8 17.9 7.8
MnO 0.15 0.5 0.1
CaO 5.2 2.4 3.5
Na?O 0.1 0.5 0.3
H?O 0.001 0.004
K (ppm) 59 305 260
Core
Fe 88.1 77.8
Ni 8 8
S 3.5 14.2
Calculated relative mass
Mantle plus crust 81 78.3
Core 19 21.7
SNC (Shergottites, Nakhlites, and Chassigny meteorites)
Because SNC meteorites are relatively young, they may not represent well, the
chemistry of the ancient Martian crust. With this age discrepancy of ancient highland
rocks tested by Pathfinder and more modern SNC meteorites, a distribution difference
can be seen. Comparing different data sets from the GRS (gamma ray spectrometer), TES
(thermal emission spectrometer), Martian meteorites, and rover missions, a (Na2O + K2O)
vs. SiO2 diagram of Martian rock and dust can be composed (Fig. 7).
20
Figure 7. Diagram composed of several meteorites along with multiple orbital and lander
missions assessing the Martian regolith. From Bell (2008).
The Core
The core of Mars is the key to understanding all the processes that follow the
initial formation of the planet after accretion. Because we have no seismic equipment on
the surface to obtain a more accurate thickness, the use of two extremes of density is
necessary to bracket a size and mineralogy. The first density extreme is a core composed
mainly of iron, but also rich in oxygen and sulfur. Mars? core has a radius of 2,200 km
and has a bulk density of 6 g/cm3. The other density extreme is a mixture of iron-nickel
alloy with a radius of 1,300 km and a bulk density equal to 8 g/cm3 (Boyce 2002).
Analysis from the Pathfinder mission had similar results of between 1,300 and 2,000 km
for the core radius (Golombek et al. 1999). The sulfur content of the core is the defining
characteristic of whether a planet can generate a magnetic field and how long that field
21
will last. The presence of sulfur lowers the freezing point of iron below the convection
temperature needed to sustain a dynamo (Stevenson 2003). If the core of Mars were to
contain >15% sulfur, then the magnetic field would be present to this day due to the
persisting activity of the dynamo (Boyce 2002). Again with the use of the Mars Global
Surveyor instruments (a magnetometer and electron reflector), scientists found this was
not the case for Mars. There are large regions of lava flows without magnetic orientation
dating to ~3 to 4 b.y., thus reiterating that the Martian dynamo ceased early in Martian
history. For this to be the case, a comparison of the SNC meteorites yields a core of
mostly iron, 7-8% nickel and about14% sulfur (Sohl and Spohn 1997). This amount of
sulfur would allow for a partially molten core to last for approximately 1 billion years.
The cause of the relatively fast core cooling is attributed to the size of Mars. The core
reached a stage where conduction and not convection became the dominant source of
heat flow (Williams and Nimmo 2004). At this time, the dynamo would have ceased to
function and no remnant magnetism could be left behind in the geologic record.
The Mantle
The thickness of the Martian mantle is directly related to the size of the core. For
example, a larger core would require a thinner, less dense mantle contrasting with a
smaller core having a thicker, denser mantle. With a range in core size and density, the
mantle thickness can only be narrowed to a window of 1,500 to 2,100 km and an average
density of 3.41 to 3.52 g/cm3. This is considerably higher than the 3.31 g/cm3 average for
the mantle of the Earth (Boyce 2002). The higher density is thought to correspond with
the amount of iron oxide present in the mantle. The crystalline structure of rocks can be
altered with the addition of heat and pressure. Therefore, it is not uncommon for layers to
22
have the identical chemistry, but due to increasing pressure a different more compact
crystalline lattice is formed. Lab experiments show that conditions like those below 1,600
km, the Martian mantle would produce high-density iron rich minerals like majorite and
spinel (Bertka and Fei 1998). With a core larger than 1,600 km, the inner most layer of
the mantle could not exist. Above the 1,600 km depth, majorite and spinel would
transform into other minerals with equivalent compositions with lower density and
greater volume. Breuer et al. (1996) use mineralogy to explain Mars? long-term
volcanism. At 1,600 km, the transition of olivine to ?-spinel and ?-spinel to ?-spinel
could generate a few strong super plumes in the Martian past, which can be seen on the
surface today (Williams and Nimmo 2004). Because the upper mantle is the source for
most magma, the composition of volcanic rock should be the same as that of the upper
mantle. Without the effects of plate tectonics, a process apparently absent on Mars, the
crust and upper mantle cannot be recycled as they are on Earth. As a result, the melts
located in the upper mantle grow progressively denser due to igneous differentiation.
Through this process, the density of the upper and lower mantle becomes homogenous
(Halliday et al. 2004)). Other geologic land features found on the surface provide insight
to the makeup of the upper mantle as well. Numerous shield volcanoes such as Olympus
Mons, Tharsis Montes, and Elysium Mons can cover thousands of kilometers at their
bases. These low viscosity flows reflect the high-iron, low-silicon composition of their
upper mantle source.
23
The Crust and Soil
The uppermost and most familiar layer of Mars is the crust. Due to differentiation
and lower temperatures, the crust is the least dense of the three main layers and is
relatively rigid. Isotropic signatures from SNC meteorites lend to a mixture of basaltic
and granitic rock (Jagoutz 1989).
If the dust samples examined by using a X-ray fluorescence spectrometer on the
Viking 1 (1976) and an alpha proton X-ray spectrometer on Pathfinder Sojourner (1997),
represented the broad average of upper crust composition, then basaltic, volcanic rock
and evaporated salts reign over the landscape (Rieder et al. 1997). Visual evidence from
the Viking sites 1 and 2 suggests iron and magnesium rich basaltic rock. The composition
of the fine grained drift soil samples did correspond with the low SiO2 (44.1 to 47.0%)
and elevated iron Fe2O3 (18.3 to 20.1%) of mafic igneous rock, but low CaO (5.6 to
6.4%) and extremely low Al2O3 (7.3 to 8.4%) are not typical of terrestrial mafic volcanics
(Cattermole 2001). The suggestion that the soils may be a mixture of Fe-rich smectite
clay, carbonates, and sulfates would be typical weathering of volcanic glasses (Toulmin
et al. 1977). Rocks analyzed using the 1997 Pathfinder?s IMP (Imager for Mars
Pathfinder) spectral analyzer yielded mixed results. Compositions varied from
conglomeritic sedimentary deposits to columnar basalt or andesitic structures. Four
spectral classes were devised: (1) grey- reflective peak at 750 nm consistent with weakly
weathered Fe2+ rocks; (2) red- high reflectance at short wavelength, but comparable 750
nm for long wavelengths and contain more ferric minerals than grey rocks; (3) pink- high
reflectivity at all wavelengths 750 ? 800 nm and are identified by encrusted drifts; and (4)
maroon- compared to pink rocks, they are darker in all wavelengths peaking at 800 nm
24
and originate from ferric-rich coatings (Cattermole 2001). In 1997, five rocks were tested
by Pathfinder for composition and compared to a sulfur-free rock. Pathfinder?s results
indicate andesitic basalt, rich in silicon and aluminum (Table 2).
Table 2. Analysis of weight % of five rocks from the Pathfinder Lander Site. From
Cattermole (2001).
Rock
A-3 Barnacle
Bill A-7 Yogi
A-16
Wedge
A-17
Shark
A-18 Half
Dome
Sulfur-free
rock
Na?O 3.2 ? 1.3 1.7 ? 0.7 3.1 ? 1.2 2.0 ? 0.8 2.4 ? 1.0 2.6 ? 1.5
MgO 3.0 ? 0.5 5.9 ? 0.9 4.9 ? 0.7 3.0 ? 0.5 4.9 ? 0.7 2.0 ? 0.7
Al?O? 10.8 ? 1.1 9.1 ? 0.9 10.0 ? 1.0 9.9 ? 1.0 10.6 ? 1.1 10.6 ? 0.7
SiO? 58.6 ? 2.9 55.5 ? 2.8 52.2 ? 2.6 61.2 ? 3.1 55.3 ? 2.8 62.0 ? 2.7
SO? 2.2 ? 0.4 3.9 ? 0.8 2.8 ? 0.6 0.7 ? 0.3 2.6 ? 0.5 0
Cl 0.5 ? 0.1 0.6 ? 0.2 0.5 ? 0.2 0.3 ? 0.2 0.6 ? 0.2 0.2 ? 0.2
K?O 0.7 ? 0.1 0.5 ? 0.1 0.7 ? 0.1 0.5 ? 0.1 0.8 ? 0.1 0.7 ? 0.2
CaO 5.3 ? 0.8 6.6 ? 1.0 7.4 ? 1.1 7.8 ? 1.2 6.0 ? 0.9 7.3 ? 1.1
TiO? 0.8 ? 0.2 0.9 ? 0.1 1.0 ? 0.1 0.7 ? 0.1 0.9 ? 0.1 0.7 ? 0.1
FeO 12.9 ? 1.3 13.1 ? 1.3 15.4 ? 1.5 11.9 ? 1.2 13.9 ? 1.4 12.0 ? 1.3
OS 92.7 85.9 97.1 88.3 92.6
Key: OS=Original sum of oxides prior to normalization. All iron is reported as FeO.
Calculated weight % norm assumes a molar Fe3O2/FeO ratio of 0.026 (Avg. Shergottite
value McSween and Jarosewich 1983).
During 1997, soil samples were also studied by instruments on Pathfinder
Sojourner. Using 15 geological filters at 12 wavelengths, these soils were classified into 4
distinct spectral classes: (1) dark soil - dune forms and is the lowest reflective material;
(2) bright soil - shallow aeolian deposits characterized by oxidized ferric rich material;
(3) lamb-like soil - occurs near ?lamb rock;? and (4) disturbed soil - created by rover
tracts (Cattermole 2001). By using three different modes, alpha, proton, and x-ray, a high
degree of accuracy could be obtained (Table 3).
25
Table 3. Chemical composition in weight % of six soils from Pathfinder landing site.
From Cattermole (2001).
Soil A-2 A-4 A-5 A-8 A-10 A-15
Na?O 2.3 ? 0.9 3.8 ? 1.5 2.8 ? 1.1 2.0 ? 0.8 1.5 ? 0.6 1.3 ? 0.7
MgO 7.9 ? 1.2 8.3 ? 1.2 7.5 ? 1.1 7.1 ? 1.1 7.9 ? 1.2 7.3 ? 1.1
Al?O? 7.4 ? 0.7 9.1 ? 0.9 8.7 ? 0.9 9.1 ? 0.9 8.3 ? 0.8 8.4 ? 0.8
SiO? 51.0 ? 2.5 48.0 ? 2.4 47.9 ? 2.4 51.6 ? 2.6 48.2 ? 2.4 50.2 ? 2.5
SO? 4.0 ? 0.8 6.5 ? 1.3 5.6 ? 1.1 5.3 ? 1.1 6.2 ? 1.2 5.2 ? 1.0
Cl 0.5 ? 0.1 0.6 ? 0.2 0.6 ? 0.2 0.7 ? 0.2 0.7 ? 0.2 0.6 ? 0.2
K?O 0.2 ? 0.1 0.2 ? 0.1 0.3 ? 0.1 0.5 ? 0.1 0.2 ? 0.1 0.5 ? 0.1
CaO 6.9 ? 1.0 5.6 ? 0.8 6.5 ? 1.0 7.3 ? 1.1 6.4 ? 1.0 6.0 ? 0.9
TiO? 1.2 ? 0.2 1.4 ? 0.2 0.9 ? 0.1 1.1 ? 0.2 1.1 ? 0.2 1.3 ? 0.2
FeO 6.6 ? 1.7 4.4 ? 1.4 7.3 ? 1.7 3.4 ? 1.3 7.4 ? 1.7 7.1 ? 1.7
OS 68.6 78.2 89.1 99.2 92.9 98.9
(OS)= Original sum of oxides prior to normalization, normalized to 98%
With the addition of the Mars Global Surveyor?s thermal emission spectrometer,
corresponding results were found with basaltic material in the ancient southern highlands
and andesitic material in the younger northern lowlands. These satellite and rover data
sets will be compared to assess deposition and/or alteration of minerals through Martian
history.
26
THE GLOBAL ESCARPMENT
Mars has a crustal dichotomy that is defined by abrupt differences in composition
and elevation between the southern highlands and the northern lowlands. This global
escarpment is unique in the solar system in that it girdles a major planet. The global
escarpment is by far the largest feature on the Martian surface visually spanning more
than 10,000 km in the eastern hemisphere. If it were present in the western hemisphere, it
is now masked by volcanic flows of the Tharsis region. Slopes along the escarpment
range from 20 to 30? with neighboring debris aprons and flow fronts sloping between 1 to
6? (Carr 2001).
Endogenic Processes
Internal (endogenic) models such as mantle or long-wavelength convection could
have caused the formation of the escarpment (Nimmo and Stevenson 2001). According to
Nimmo and Stevenson (2001), degree-1 mantle convection develops in a planet with the
core size and planetary radius of Mars. Physical properties vary at depth, such as a
mineralogical phase change or temperature- and pressure-dependent viscosity; these
would drive a long-wavelength perturbation and cause it to be the fastest growing
structure in the lower mantle. Two plausible explanations arise from degree-1 mantle
convection in order to explain the escarpment. First, the primitive planet has yet to form a
crust at all. Mantle upwelling in the form of a super plume solidifies to become the
primordial crust and thickens over time to become the southern highlands (Roberts 2004).
27
Alternatively, lithospheric thinning by vigorous mantle convection could have caused a
lowering of the entire northern hemisphere (Wise et al. 1979b; Fig. 8). All convection
models assume a crustal thickness of approximately 50 km (Zuber et al. 2000). Another
endogenic process such as plate tectonics would involve the spreading of the Borealis
Basin. Through this process, crustal subduction under the southern highlands could have
caused the escarpment (Sleep 1994).
Figure 8. Example of degree-1 mantle convection plume model. From Roberts and Zhong
(2006).
Exogenic Processes
External (exogenic) processes are the other competing possibility for the
escarpments origin. Extra-planetary sources such as comets or asteroids are one way to
change the surface of a planet. Wilhelm and Squyres (1984) proposed that a single giant
impact would have formed a basin ~ 7,700 km in diameter, centered at 50?N 190?W.
28
Later, others such as Andrews-Hanna et al. (2008) proposed an impact ellipse measuring
approximately 10,600 by 8,500 km, centered at 67? N, 208? E (Fig. 9). If the impact
origin of the Northern Basin of Mars is correct, such a crater would dwarf any other in
the solar system by a factor of two (Table 4).
29
Figure 9. Views of the Borealis Basin: (a) polar projection around the basin center at
67? N, 208? E, showing the present-day topography and shaded relief of Mars; (b) the
modeled crustal root; (c) the modeled topographic gradient; (d) traced dichotomy
boundary is shown and compared with the best-fit ellipse (southern boundary of Arabia
Terra denoted by dashed line); (e) outlines of the northern and southern edges of Arabia
Terra (dotted lines; approximated using a threshold crustal thickness) are shown over a
crustal thickness map along with the reconstructed basin rim required to restore the
crustal thickness in Arabia Terra to the mean highlands value; (f) reconstructed crustal
thickness before basin modification in Arabia Terra. From Andrews-Hanna et al. (2008).
30
Table 4. List of largest known impact basins in the Solar system. From USGS 2010a
Planetary Nomenclature. (Accessed on 12 Jan., 2010).
Name Location Size (diameter)
1 Aitken basin Moon 2,500 km
2 Hellas Basin Mars 2,100 km
3 Skinakas Basin Mercury ~1,600 km
4 Caloris Basin Mercury 1,550 km
5 Mare Imbrium Moon 1,100 km
6 Isidis Planitia Mars 1,100 km
7 Mare Tranquilitatis Moon 870 km
8 Argyre Planitia Mars 800 km
9 Mare Serenitatis Moon 700 km
10 Mare Nubium Moon 700 km
11 Beethoven Mercury 625 km
12 Valhalla Callisto 600 km, rings to 4,000 km diameter
13 Hertzsprung Moon 590 km
14 Turgis Iapetus 580 km
15 Apollo Moon 540 km
16 Huygens Mars 470 km
17 Schiaparelli Mars 470 km
18 Menrva Titan 440 km
19 Korolev Moon 430 km
20 Dostoevskij Mercury 400 km
21 Odysseus Tethys 400 km
22 Tolstoj Mercury 390 km
23 Goethe Mercury 380 km
24 Tirawa Rhea 360 km
25 Mare Orientale Moon 350 km, rings to 930 km diameter
26 Epigeus Ganymede 340 km
27 Gertrude Titania 320 km
28 Asgard Callisto 300 km, rings to 1,400 km diameter
29 Vredefort crater Earth 300 km
*There are approximately twelve more unnamed impact craters/basins larger than 300 km on the Moon,
five on Mercury, and four on Mars.
The largest and most complex impact related structures are called multi-ring
basins. They contain concentrically oriented radial rings with inward facing scarps
(Melosh 1989). Multi-ring basins on Mars are divided into three groups depending on the
31
increase in diameter of the basin: (1) 300 < D < 1850 km; (2) 1850 < D < 3600 km; (3) D
> 3600 km (Schultz and Frey 1990). Variations in multi-ring basin morphology may be
related to lithospheric thickness, mechanical interactions between the basin-forming
impacts, or the spherical geometry of the target (Schultz and Frey 1990). Theoretical
models of large impact structures suggest that basin topography and the formation of
concentric rings can differ due to post impact relaxation (Melosh 1982). Therefore, older
basins are structurally and morphologically different than younger crater basins. Basin
rings can be inferred by topography, channel geometry, and the distribution of radial
concentric structures (Schultz et al. 1982). Past studies have used the Orientale basin,
located on the Moon, as a template for all multi-ring basins of any planet (Head 1974).
Orientale is the youngest and best preserved multi-ring basin and has not changed
geomorphically since its formation ~3.85 billion years ago (Wilhelms 1987).
Lithospheric thickness is an important factor in the development of concentric basin
structure (Melosh and McKinnon 1978). With a relatively thin crust, post crater
relaxation will dominate and topographic features will remain subdued, on the contrary,
with a much thicker crust, the relaxation is limited allowing for the crater rim and ring
structures to be more pronounced. Therefore, if the northern basin is an impact feature
depending on the crustal thickness at the time of impact, we would expect to see some
remnants of radial rings and inward facing scarps along the global escarpment.
More recent impact models have been developed using computer software and
have evolved to reveal the pre-existing Martian crust before the Tharsis bulge had
developed (Andrews-Hanna et al. 2008). One such model extrapolates the Borealis Basin
as an elliptical shape suggesting an oblique impact from a large celestial object in early
32
Martian history (Andrew-Hanna et al. 2008; Fig. 10). During a mega-impact, the crust
would have been thinned because of ballistic transport and the escarpment would
represent the resulting crater rim (Marinova et al. 2008). Other elliptical basins are
present on Mars such as Hellas and Utopia.
33
Figure 10. Cylindrical projections of: (a) topography (MOLA data) and (b) crustal
thickness from Neumann et al. (2008) of Mars. Main features labeled in a include Tharsis
(Th), Arabia Terra (AT), Hellas (H), Argyre (A), and Utopia (U), as well as the Borealis
basin outline proposed by Wilhelms and Squyres (1984). In these cylindrical projections,
crustal thickness was modeled with perturbation (isostatic root) showing continuation of
the dichotomy boundary beneath Tharsis; (c) The observed dichotomy boundary (thin
line) is compared with the best-fit ellipse (bold line). The break in slope separating
Arabia Terra from the highlands is shown as a dashed line. From Andrews-Hanna et al.
(2008).
34
The shape of the Borealis Basin has been under scrutiny by mantle convection
advocates (e.g. Zuber et al. 2000) since the early exploration of the dichotomy. The
irregular shape of this basin does not conform to typical impact features that leave either
a circular or elliptical crater. One explanation is that multiple impacts are responsible for
the irregular shape of the basin. By overlapping several large basins that formed early in
the Martian past, the pattern of knobby/fretted material in the form of ancient crater rims
would coincide with these impacts (Frey and Schultz 1998).
35
THE FRETTED TERRAIN
The fretted terrain is located along the global escarpment +/- 10? from 40? N
latitude and confined between 280? to 350? longitude (Sharp 1973). The steep walled
escarpment traces a somewhat irregular course along the southern boundary of the terrain
beginning the planimetric pattern associated with the fretted terrain (Fig. 11). In some
places, the terrain is dissected by flood channels growing wider northward and there are
numerous island-like outliers who resemble butte and mesa structures.
Figure 11. Map showing the location of the fretted terrain used in this project. Modified
from USGS MOLA DEM (1999).
36
The time frame for the formation of the fretted terrain either coincides with its
initial formation or is a product of an evolving scarp over time. During early Noachian,
internal forces consisting of mantle convection or plate tectonics could have initially
formed the terrain. If mantle convection created the global escarpment along with the
fretted terrain, then the tops of these blocks should dip toward the northern lowlands as a
product of crustal relaxation to fill the lower lying areas to maintain isostasy. External
forces like single or multiple impacts creating a crater wall and terrace structure could
have produced this type of terrain as well. This terrace effect would cause these fretted
blocks to slope toward the southern highlands (Grieve 1987; Fig. 12). If an oblique, large
impact were the scenario, then the terrace would not only tilt back toward the escarpment,
but also tilt away from the original direction of the impactor.
Figure 12. Example of terrace formation due to a large meteor impact at zero on the
horizontal scale. From Morgan et al. (2000).
During Hesperian, the fretted terrain could have been caused by rifting following
a linear crack which is prominent during this epoch, or it could be an erosional feature,
such as a winding channel, due to intense runoff corresponding to the chaotic terrains that
are present in the eastern region of Valles Marineris. If the formation of the fretted terrain
37
occurred during Amazonian such processes might involve either ice wedging or slumping
and calving analogous to ice-wedging polygons (Sharp 1973; Fig. 13). The fretting
process as defined by Sharp is ?the receding of a steep scarp by undermining or sapping
mechanisms, maintaining its steepness but developing a complex planimetric
configuration.? By this process, a smooth, flat floor is created with isolated buttes and
mesas.
Figure 13. Image of terrestrial, local scale, ice-wedge polygons located in Barrow,
Alaska. From Lucchitta (1980).
Another proposed formational process for the escarpment and fretted terrain could
be the representation of a huge paleoshoreline (Parker et al. 1993). Vastitas Borealis is
extremely smooth like the abyssal plain of Earth?s oceans and the volume of water
required to fill the basin is within the upper boundary of availability early in the Martian
38
history (Cattermole 2001). Below contact 2 most surfaces are smooth, indicative of
abyssal plain deposits, whereas contact 1 encompasses rougher terrain and could
potentially be a short interval of a Martian sea-level high-stand (Parker et al. 1993; Fig.
14).
Figure 14. Mars northern polar view: (a) Lambert equal area projection of MOLA
Northern Pole-to-equator topography from Smith et al. (1999). Black lines indicate
positions of contacts interpreted to be shorelines; (b) Major features as seen in (a). From
Head et al. (1999).
Depending on the slope orientation of the fretted-terrain blocks, inferences and
comparisons can be made about the possible formation and continuing geomorphic
processes. Dips toward the lowlands would involve crustal relaxation and /or sapping and
mass wasting over time. Horizontality or little dip to the top of each block would indicate
thermokarst activity or a remnant ring structure. Thermokarst activity could also produce
a concave structure on the tops of the blocks. If the fretted terrain blocks dip away from
the lowlands or the majority of the blocks dip to the east or west, they could have
39
possibly been formed during a major impact in the past (as shown in Fig. 12). Because
the terrain is composed of the same rock type, the weathering processes over time should
be relatively consistent over the entire scarp. All imagery processing and modifications
will be cross-checked with other imagery data bases and then compared to past literature
for review.
40
MISSIONS AND INSTRUMENTATION
Mars Global Surveyor
Mar Global Surveyor operated by the Jet Propulsion Laboratory (JPL) arrived at
Mars on September 11, 1997 and continued to collect data until November, 2006. Its
longevity was due in part to the ingenious use of angular momentum management
implemented in August, 2001 to conserve propellant and extend the orbiters lifespan by
an additional three years. Mars Global Survey was designed to encircle the planet every
two hours in a polar orbit at an altitude of 378 kilometers (NASA 2010a). The altitude
was chosen to take advantage of a sun-synchronous orbit to obtain identical light
conditions unconstrained by the date of the corresponding data. Six scientific instruments
were mounted on the spacecraft and four were used in this study: (1) MOC ? Mars
Orbital Camera; (2) MOLA ? Mars Orbital Laser Altimeter; (3) TES ? Thermal Emission
Spectrometer; (4) MAG/ER ? Magnetometer and Electron Reflectometer; (5) USO/RS ?
Ultra-stable Oscillator for Doppler measurements; and (6) MR ? Mars Relay
MOC? Mars Orbital Camera
The Mars Orbital Camera was designed to take highly detailed images from any
orientation with respect to the horizon. It consists of two independent cameras each
supported by a 32-bit microprocessor. The narrow angle camera utilizes a 70 cm, f/10
Ritchey-Critien reflector and with two 2048-element charged couple device (CCD) is
able to resolve objects as small as 1.4 m/ pixel (Dallas 1996). Owing to the size of the
41
data set, high resolution images are black and white sacrificing color for clarity. The
wide-angle camera contains two f/6, fish eye lenses, paired with two 3456-element
CCD?s. This arrangement allowed for the acquisition of color images between 575 and
625 nm with a resolution of 250 m/pixel as MOC collected more than 240,000 images
during the life span of the instrument (MSSS 2010).
MOLA - Mars Orbital Laser Altimeter
MOLA was constructed to generate high resolution topographic profiles. With the
use of a diode-pumped neodymium-yttrium, aluminum-garnet laser and a firing rate of 10
pulses per second, MOLA was able to obtain the most accurate and complete LIDAR
(light detecting and ranging) set of any planetary body in the solar system, including
Earth. Recording the lag time between the firing and interception of the reflected laser
pulses by the 50 cm Cassegrain collecting mirror gives a precise local altitude on the
surface. Each laser spot measured approximately 160 meters in diameter and were spaced
300 meters apart (Dallas 1996). This technique yielded a range resolution of one to ten
meters up to 30? slopes, and an absolute accuracy of ~1 meter (Zuber et al. 1992). A high
resolution map composed of 27 million elevation measurements was used to create a
DEM which is the base map of topography for this study.
TES ? Thermal Emission Spectrometer
The TES was comprised of two telescopes and used to determine thermal and
mineralogical properties on the Martian surface. The larger 15.24 cm Cassegrain
telescope bolsters a two port Michelson interferometer spectrometer with a 6.25 to 50 ?m
spectral range. The smaller telescope supplies two channels (0.3 to 3.9 ?m and 0.3 to 100
?m) respectively. Because the instrument utilizes six detectors and is nadir pointed (180?
42
from the zenith), illumination values can be obtained for surface comparisons
(Christensen et al. 2001).
USO/RS ? Ultra stable Oscillator for Radio Science
A two-fold approach is used with the final MGS instrument. Observations of the
distortions, which include frequency, phase, and amplitude, of the spacecraft?s radio
signal through the Martian atmosphere can produce a high resolution temperature profile.
Also by instituting the Doppler tracking and monitoring the minute changes in the
frequency, a gravity field can be reconstructed with a high level of accuracy. The only
way to accomplish this is by providing an ultra-stable oscillator with extremely stable
frequencies for the reference. A frequency of 19.143519 MHz was chosen to limit
variations to less than 1.0 in 1010 Hz (Dallas 1996).
MRO - Mars Reconnaissance Orbiter
Orbital insertion of MRO, which is operated by JPL, was achieved on March 10,
2006. The payload for this satellite consists of six different instruments: (1) HiRISE -
High Resolution Imaging Science Experiment; (2) CRISM - Compact Reconnaissance
Imaging Spectrometer for Mars; (3) CTX - Context Imager; (4) MCS - Mars Climate
Sounder; (5) MARCI ? Mars Color Imager; and (6) SHARAD ? Shallow Subsurface
Radar. Only the first three will be discussed and used in this project. The MRO is also
operated in a sun-synchronous, polar orbit located closer to the Martian surface than
MGS only skimming the surface at altitude between 255 to 320 km (Murchie et al. 2004).
The MRO served a dual purpose with the high resolution imagery and spectrometers
aboard, it could provide instant data, but also look for potential landing sites for future
Martian missions.
43
HiRISE ? High Resolution Imaging Science Experiment
HiRISE is unparalleled for image quality, coverage, and resolution to the present
date. An aperture of 50 cm, the largest ever carried into deep space, gives a resolution of
approximately 30 cm/pixel. The images are collected in three color bands, 400 ? 600 nm,
550 ? 850 nm, and 800 ? 1,000 nm. With a lager storage capacity than previous satellites,
images can be taken in different modes increasing image sizes from a few to 28 megabits
(Graf et al. 2005).
CRISM ? Compact Reconnaissance Imaging Spectrometer for Mars
High resolution hyperspectral images were taken in the electromagnet spectrum
between 0.4 to 4.0 ?m and were used to indicate water and hydrothermal systems by
mineralogical means (Graf et al. 2005). The instrument encompasses a Ritchey-Chretien,
10 cm telescope with 2.06? field of view and two corresponding spectrometers. The light
is split inside the spectrometer with a dichroic into visible, near-infrared, and infrared
(Murchie et al. 2004). Unique to CRISM is the gimbal mounting which enables a specific
target to be track as opposed to just being in the swath path.
CTX ? Context Camera
The CTX is capable of 6m/pixel resolution using its 10.8 cm aperture. Differing
from the other instruments by more than twice the field of view of the CRISM (5.8?) and
a 5,000 pixel detector allow for a larger area to be scanned in a shorter period of time
(Graf et al. 2005).
44
Mars Odyssey
On October 24, 2001 the insertion period began for Mars Odyssey spacecraft
under the direction of Arizona State University (ASU). The satellite carried three
scientific instruments onboard: (1) THEMIS ? Thermal Emission Imaging System; (2)
GRS ? Gamma Ray Spectrometer; and (3) MARIE ? Mars Radiation Environment
Experiment (Fig. 15). Again only THEMIS is used in the present project and will be the
only instrument discussed further. Odyssey not only provides data from its payload
instrumentation, but also acted as a transmitter for the Martian rovers Spirit and
Opportunity (NASA 2010b).
THEMIS was used to investigate physical properties and mineral compositions of
the Martian surface. Collecting images in nine wavelengths in the thermal-infrared (6.8 to
14.9 ?m) and five bands in the visible/near-infrared (0.42 to 0.86 ?m) gives this
instrument the ability to function day or night with its 12 cm aperture and 100 m/pixel
resolution capability. By decreasing the resolution, a larger swath path can be achieved
thus providing the ability to map the entire surface of the planet during the lifetime of the
satellite. Because most geological materials have strong fundamental, vibration
absorption bands in the thermal-infrared part of the spectra, THEMIS should provide
insight into mineralogical compositions of the planet?s surface (Christensen et al. 2001).
45
Figure.15. Satellites that generated data used in this project: (a) Mars Global Surveyor;
(b) Mars Reconnaissance Orbiter; (c) Mars Odyssey Spacecraft. All images from NASA
2010d. (Available from http://mars.jpl.nasa.gov/gallery/spacecraft/index.html).
46
METHODOLOGY
Remote Sensing was defined by Pruitt (1962) as "The acquisition and
measurement of data/information on some properties of a phenomenon, object, or
material by a recording device not in physical, intimate contact with the features under
surveillance." For monetary reasons, remote sensing is arguably the best, current viable
way to study planetary bodies. With the advancement of technology and instrumentation,
a wealth of knowledge can be obtained through these processes. Three satellites (Mars
Global Surveyor, Mars Reconnaissance Orbiter, and Mars Odyssey; Fig. 15) were used in
the study, each with multiple instruments to gather information on Mars. Imagery was
used to digitize and map the location, shape, and orientation of the global escarpment and
fretted terrain. In addition, MOLA data will be used to map the profile of the
corresponding fretted terrain and escarpment to help determine slope stability. This
information along with mineralogical data will potentially give us evidence that the
Borealis Basin was formed by either endogenic or exogenic processes.
Data Extraction
The initial stage of this project involved a survey of the global escarpment and
fretted terrain using Google Earth 5.0. Three dimensional global projections can be
represented by using this type of software. The tilt and zoom can be adjusted allowing for
any aspect or orientation to be analyzed. An application for the planet of Mars gives
access to six global maps including Visual, MOLA, Daytime Infrared, Nighttime
47
Infrared, Viking Color, and MDIM 2.1which provide a quick reference to the surface of
Mars. There is also an imagery data base of five orbital satellites: (1) HiRISE; (2) CTX;
(3) MOC; (4) HRSC; and (5) CRISM with the ability of image importation and overlay
allowing multiple applications to be presented simultaneously. Images from these orbiters
can be extracted by turning on the corresponding satellite function and clicking on the
image of interest. This application will connect you to one of the many websites where
the data-base of images is located. From these databases, files can be downloaded, saved
as a tiff file, and imported into Google Earth for overlay and rectification. Examination
and processing of these maps and images will provide a three dimensional, interactive
map for detailed quantitative analysis. An example of one of the maps used to research
the proposed area is provided in Figure 16.
48
Figure 16. Applications in imagery overlays in Google Earth 5.0.
Any planetary study must first begin with an accurate base map. The United
States Geological Survey (USGS) website (1999)
(fttp://pdsimage2.wr.usgs.gov/pub/pigpen/mars/mola/) offers a wealth of data-bases from
which files can be downloaded. MOLA data are the most complete topographic data set
that is currently available of Mars. For this reason, it makes an excellent base map for
which all other data can be positioned. The simple, cylindrical projection used for MOLA
data was acquired from the USGS site with the file name
(mola128_88Nto88S_Simp_clon0)zip. The MOLA data set is a digital elevation model
raster data set which contains information in x, y, and z coordinates for each pixel
49
providing a three dimensional map that can be imported into GIS for detailed analysis of
topography including elevation profiles, slope, and orientation of morphology.
Additional data were collected from the USGS Planetary GIS Web Server, the
Planetary Interactive G.I.S.-on-the-web Analyzable Database (PIGWAD)
(http://webgis.wr.usgs.gov/pigwad/maps/index.html). The database incorporates a
multitude of capabilities for image processing and analysis. The layers involved for this
project include: (1) Mars Orbiter Laser Altimeter (MOLA); (2) Mars Orbital Camera
(MOC); (3) Mars Reconnaissance Orbiter (MRO); and (4) Mars Odyssey Mission
(THEMIS-Thermal Emission Imaging System). These layers can be accessed in
PIGWAD using the select by line/polygon tool to draw a line across an area of particular
interest. Any image that is crossed by that corresponding line will then be available as a
tiff file for analysis in GIS.
The Arizona State University website (http://mars.asu.edu/data/) provides access
to many other data sets that have been acquired from various orbiting satellites and were
used for downloading corresponding images.
Data Incorporation
A three dimensional global projection map was used in Google Earth (GE) 5.0.
The layers that were used in this project included the MOLA, MDIM 2.1, and Visible
because they are the highest resolution maps that cover 100% of the planet?s surface.
Once the images were extracted, they were overlain and rectified to the correct position
on the global projection using the stretch and transparency functions that is incorporated
with the overlay tool in GE. Using this process, a mural was composed of 171 context
50
camera images (CTX) aboard the Mars Reconnaissance Orbiter covering more than 80%
of the entire visual escarpment and fretted terrains (Fig. 17).
Figure.17. MDIM 2.1 and visible map with image overlays from context camera in
Google Earth 5.0.
After the MOLA data set has been extracted from the USGS website, it can then
be processed in GIS. First and foremost, since the study involves a celestial body other
than Earth, the projection must be defined so the data line up properly in GIS that
accounts for the size and shape of Mars. After adding the MOLA data to GIS (in this case
ArcGIS 9.2) projection can be defined with a few commands (see Appendix 1). This
allows the user to set the geoid, or in this case aeriod, to the current Martian projection
system. From here, the linear unit was set to kilometers due to the large sizes of the
51
fretted terrain blocks. Finally, a coordinate system is selected: Select>>Solar
System>>Mars 2000.prj. This sets the aeroid to the base coordinates of the MOLA data
(semi-major axis = 3,396.19 km, semi-minor axis = 3,376.20 km) for use in GIS. Figure
18 illustrates the MOLA data in ArcGIS 9.2 with the data frame properties window open.
Figure 18. Defining projection of MOLA digital elevation model in ArcMap 9.2.
Using the MOLA data, a slope map was produced using the spatial analyst feature
(see Appendix 1). Using the base map, slopes are calculated to a particular degree with a
z factor = 1 and a cell size of 463.0836 meters. This will provide a ratio for inclination
and slope stability (maximum angle of repose) that will be discussed later. A contour line
and aspect (orientation as defined by north) can be extracted using the same spatial
analyst tool. Owing to the size of some of these data sets (>10 GB), multiple maps were
52
generated for specific individual analysis. These maps are a vital part in the assessment of
the global escarpment and fretted terrain. Depending on the formation and evolution of
the fretted terrain, slope stability and directional orientation toward the sun could provide
evidence of mass wasting and/or thermokarst activity.
Unprojected Mars global data sets from The Arizona State University website
(http://mars.asu.edu/data/) are processed through a procedure termed georeferencing
which allows for overlay of imagery with the MOLA base map. New unprojected
imagery is added to GIS along with the rectified MOLA base map. Using the
georeferencing tool in ArcGIS 9.2, ground control points (GCPs) can be added to the new
map and then matched to the corresponding GCPs of the original base map (see also
Appendix 1). The four corner controls points are sufficient to accurately georectify the
imagery. This application was repeated for 25 overlays of imagery representing
mineralogy, roughness, and albedo, among others.
Analysis Techniques
After the processing of all maps, data sets, and imagery; geospatial analysis
proceeded. First, the global escarpment had to be established as a linear feature for the
purpose of future comparisons and techniques. For this method, a shape-file was
produced using ArcCatalog 9.2 (see Appendix 1) and added to the existing map. Using
the editor tool in ArcMap, the escarpment was Heads-up digitized. Once in an editing
session, the escarpment was digitized by selecting vertices using the slope map generated
earlier. The slope angle of > 20? was used due to the maximum average angle of repose
on Earth is roughly 40? for talus/regolith and since MOLA data resolution is 463 m? per
pixel. With these two factors in mind, an average of 0 to 40? is 20? and therefore was
53
used to delineate the escarpment. The global escarpment was split into three different
sections (northern low escarpment, northern escarpment, and southern escarpment) each
with an individual shape-file in order for differing techniques to be processed later, such
as buffers, orientations, and sizes of blocks. This will allow for the assessment of
modification processes such as fluvial and eolian transport along with thermokarst
activity depending on elevation and latitude.
The fretted terrain was considered as individual blocks for this study and could be
classified as polygons accordingly. Since there are approximately 700 blocks to classify,
the most efficient way to achieve this is by creating a personal geodatabase. This can be
performed using ArcCatalog and allows you to incorporate multiple datasets into the
same database (see Appendix 1). Finally, within each feature data set, new feature classes
(in these instances, polygons) can be created again splitting the data into smaller, more
discrete manageable pieces. The creation of personal geodatabases utilize topology and is
a time saving technique for once the feature datasets are established, a table is
constructed in the personal geodatabase feature class incorporating identification, length,
and area for each polygon. After the feature datasets have been added to the map, the
polygon creation can then commence utilizing the same technique for establishing the
global escarpment for digitizing the blocks. Due to the vast differences in elevation
traveling east to west along the escarpment, the fretted blocks were split into two
different sections (blk- northern fretted terrain and polynorth- northern low fretted
terrain) for analysis. Differences in elevation would play a deciding role as to how steep
the potential debris aprons around the blocks can be and the possible interaction with
ancient oceans as shore lines in the past as well as other geomorphological processes. The
54
classification scheme created to differentiate between a block or mesa and a knob or
mound is as follows: (1) blk- a horizontal congruency of < 2? slope between adjacent
pixels located on the top of the block and the perimeter of each block must be surrounded
by pixels with at least 50% >20? and 75% >16? and; (2) polynorth- a horizontal
congruency of < 2? slope between adjacent pixels located on the top of the block and the
perimeter of each block must be surrounded by pixels with at least 25% >20?, 50% >16?,
and 75% >12?. The two part classification scheme was used due to differing elevations of
the two block groups which could promote different formational and erosional
circumstances in the past. Blocks located at higher latitudes would have a greater
probability of ice accumulation during the Martian seasons and processional cycle
leading to faster erosion and lower angle debris aprons. With this established, digitization
of each individual polygon was performed using an editor session in ArcMap accruing
580 blk and 132 polynorth polygons.
After the polygons were created, the center of mass had to be established in order
to produce a center point for which long and short axis could be drawn. The
corresponding lengths of the axis provide insight into orogenic and evolutionary
processes. Extensional forces whether they are internally or externally driven would
provide a plane of failure that would roughly mimic the corresponding escarpments
orientation lending to greater average variation in the length vs. width ratio > 2:1. If
water driven erosion were the culprit for the formational patterns, a dendritic pattern
which is much more erratic can be deduced and the polygons would have an irregular
shape. Finally, if ice wedging is the only cause for the formation of the fretted blocks, an
average ratio of no greater than 2:1 would result as compared to similar blocks in higher
55
latitudes on Earth (see Fig. 13). ArcGIS has the ability for the use of scripts and tools for
more customized applications. One such tool is Easy Calculator 5.0
(http://www.ian-ko.com/) which provides a variety of features for data
extraction/organization for points, lines, and polygons. Using this tool, a center of mass
for each polygon can be extracted (Fig. 19; see also Appendix 1). Once a center of mass
is established axes can be drawn through the point to assess length vs. width ratios of
these blocks. These shape-files (lines) can be exported as new feature classes in the
featured datasets of existing personal geodatabases. Axes for each polygon were digitized
perpendicular to one another in this process. Another tool can be incorporated with the
axes to obtain compass bearing (see Appendix 1). With this process, length and
orientation of these lines can be found which could possibly help determine orogenic
processes. Again, assessment of the axes for random orientations or corresponding
directions would provide evidence of either extensional or mass wasting processes. Once
the long axis length has been computed, +90? can be added to the corresponding long axis
for the orientation of the short axes.
56
Figure 19. Geoprocessing of MOLA data for extraction of fretted terrain.
57
RESULTS
Regional Analysis
After insertion and rectification of the MOLA DEM base map in ArcGIS
quantitative and qualitative analysis began. Regional scale was classified as
interpretations made along any transect of > 500 km. The escarpment was split into two
regions (northern- 280? to 325? and northern low- 325? to 350?) for this study on the
criteria of elevation changes found along the boundary. The boundary line for the
escarpment was traced along the greatest southerly extent with a slope of >20?. The
change in elevation along the 1,884.8 km northern escarpment was approximately 2,400
meters with the greatest elevation of +1,039 meters around 27? 31?N, 284? 27? and lowest
-1,377 meters around 43? 20?N, 323? 16?. The general dip in elevation followed a
symmetric east to west pattern. Elevation differences along the 2,314.4 km northern low
escarpment was at least -687 meters around 41? 12?N, 327? 25? and at most -3,618 meters
around 44? 28?N, 345? 35?, which demonstrated a difference of almost three kilometers
from east to west. The 4,968.8 km southern escarpment ranged from +878 meters around
8? 24?N, 262? 54? to -1,334 meters around 2? 8?N, 228? 7?. There are variable fluctuations
in the elevation, but the general trend here was roughly horizontal with no more than a
few hundred meters of difference in elevation from east to west along the transect.
The northern escarpment primarily follows the division between the Noachian
cratered plateau material (Nplc), Noachian hilly cratered material (Nhc), and Hesperian
58
knobby material (HNk). These two Noachian aged units were coeval with the early
formation of the feature and the later erosion that takes place. Structurally the crust
averages between 40 to 50 km thick, along this section of the escarpment suggesting a
deeper seeded mechanism of origin rather than simple topology.
The southern escarpment was more erratic in that there was moderate symmetry
as it followed the Noachian cratered plateau material (Nplc) and Hesperian knobby
material (HNk), but there were intermingled units of Hesperian rolling plains material
(Hpr) and Amazonian cratered plains material (Apc) that cut across the traced escarpment
boundary. The crustal thickness of this section is between 50 and 60 km (Fig. 20).
59
F
igure
20. (
a) G
eologi
c Map
of Mar
s includi
ng t
he
northe
rn
esc
arpme
nt.
(W
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ne
de
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ates
esc
arpme
nt boundar
y li
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).
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ge
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d f
rom S
cott
and Car
r (
1978)
.
60
Figure
20. (
b) Ge
ologi
c Map
of Mar
s includi
ng t
he
sout
he
rn e
sca
rpme
nt.
(W
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e li
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de
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ate
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carpme
nt bounda
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).
Ima
ge
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rom S
cott
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r (
1978)
.
61
c. Mode
led Fi
gure
20.
(c
) Mode
led
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ss m
ap (0.5
pixel/deg
ree
), (W
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.
Ima
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- H
anna
et al. (
200
8).
62
Topographic cross sections were obtained using the previously incorporated DEM
in ArcGIS corresponding with the earlier work of Andrews-Hanna et al. (2008) and
Kiefer (2008) showing along the escarpment there are elevation changes of over 3 km
over distances of <100 km depending on location. Other comparisons were made using
the steep cliffs of Valles Marineris and the relic crater rims of Hellas and Argyre which
can be found on the Martian surface (Fig. 21).
63
Figure 21. Cross sections along the entire global escarpment: (a) Two regional cross
sections of the northern low global escarpment; (b) Two regional cross sections of the
northern global escarpment; (c) Two regional cross sections of the southern global
escarpment (scale = meters).
64
Regional mineralogy shows a distinct transition zone that is located
approximately along the global escarpment boundary. Basaltic rocks are the dominant
rock type south of the dichotomy in the highlands resulting from massive volcanic floods
in the past, whereas andesite is more prevalent in the northern basin lending to a differing
origin either from possible fissure filling due to crustal contracting or from excavation
and mantle refilling due to a large impact (Fig. 22).
65
Figure 22. Intensity value map derived from TES mineralogical data: (a) basalt; (b)
andesite (4 pixel/degree. White line delineates global escarpment). Images from Arizona
State University, Mars Global Data Sets (2006).
66
Eight other regional maps were composed to gain a broader sense of the
mineralogy. These maps are vital in assessing orogenic and evolutionary processes on a
global scale for Mars. Bowen?s reaction series is a classification scheme used to
determine the silica content of magma at the time of cooling. Group 1 is the
discontinuous series of Bowen?s reaction series, whereas group 2 is the continuous
reaction series (Fig. 23). These maps show the differentiation of the silica and possible
cooling rate of the magma that was present at the time of deposition/intrusion and
correspond with that mineral type.
67
Figure 23. (Group 1a-b) Bowen?s discontinuous reaction series including quartz acquired
from TES mineralogical data: (1a) olivine; (1b) clinopyroxene. White line delineates
global escarpment. Images from Arizona State University, Mars Global Data Sets (2006).
68
Figure 23. (Group 1c-d) Bowen?s discontinuous reaction series including quartz acquired
from TES mineralogical data: (1c) amphibole; (1d) quartz. White line delineates global
escarpment. Images from Arizona State University, Mars Global Data Sets (2006).
69
Figure 23. (Group 2a-b) Bowen?s continuous reaction series including hematite acquired
from TES mineralogical data: (2a) plagioclase; (2b) feldspar. White line delineates global
escarpment. Images from Arizona State University, Mars Global Data Sets (2006).
70
Figure 23. (Group 2 c-d) Bowen?s continuous reaction series including hematite acquired
from TES mineralogical data: (2c) orthoclase; (2d) hematite. White line delineates global
escarpment. Images from Arizona State University, Mars Global Data Sets (2006).
71
Sectional Analysis
Sectional scale constitutes landscape sizes that are between 50 and 500 km.
Analysis of these areas include the initial break in the escarpment and the fretted terrains
located up to 300 km away. The fretted terrain was split into two corresponding sections
as was the escarpment due to elevation differences for future orogenic and evolutionary
analysis. Along the escarpment boundary and the first tier of northern fretted blocks there
are deep valleys/fractures with depths reaching 1 km and a strong linear orientation
between the long axis of the blocks and the escarpment is present. The northern low
fretted terrain blocks show no preferred orientation of the long axis as opposed to the
escarpment boundary (Table 5).
72
Table 5. Analysis of fretted terrain composed in ArcGIS 9.2
Northern fretted polygons
length (km) width (km) perimeter (km) area (km?) length vs. width azimuth
average 15.24 5.17 42.33 141.49 4.48 91.90
maximum 139.68 49.20 537.96 5246.87 49.67 180.00
minimum 1.95 0.46 8.78 1.33 1.01 0.16
distance from escarpment (km) 0-50 0-100 0-150 0-200 0-250 0-300
average total area(km?) 331.64 195.61 173.95 160.48 153.36 149.80
# of total polygons 119.00 275.00 381.00 449.00 490.00 514.00
% of polygons 20.84 48.16 66.73 78.64 85.81 90.02
0-50 50-100 100-150 150-200 200-250 250-300
average area in buffer zone (km?) 331.64 92.38 121.14 80.56 79.93 77.06
# of polygons in buffer zone 119.00 156.00 106.00 68.00 41.00 24.00
Northern low fretted polygons
length(km) width(km) perimeter(km) area (km?) length vs. width azimuth
average 22.18 8.67 67.70 355.45 3.20 103.26
maximum 143.48 58.85 721.40 10418.30 12.54 178.88
minimum 2.48 0.66 7.62 3.19 1.01 0.30
distance from escarpment (km) 0-50 0-100 0-150 0-200 0-250 0-300
average total area(km?) 887.97 597.94 441.99 378.95 367.29 362.95
average total area(km?)/
without largest block 506.75 352.43 275.72 257.99 270.65 282.50
# of total polygons 26.00 45.00 61.00 84.00 105.00 126.00
% of polygons 19.70 34.09 46.21 63.63 79.54 95.45
0-50 50-100 100-150 150-200 200-250 250-300
average area in buffer zone (km?) 887.97 99.22 126.15 211.74 320.67 341.22
# of polygons in buffer zone 26.00 15.00 20.00 23.00 21.00 21.00
These fretted valleys have flat lying bottoms that are composed of lineated valley
fill along most of escarpment (Lucchitta 1984). The northern fretted blocks also show
signs of some extensional processes with an average length vs. width ratio of ~4.5 and a
logarithmic trend of decrease in the size of the blocks traveling from south to north. The
northern low fretted blocks are on average more than twice the size of the northern blocks
and show less if any signs of extensional processes with a length to width ratio of ~3
along with a logarithmic trend of decrease in the size of the blocks (Fig. 24).
73
Figure 24. Chart showing size distribution on both classes of fretted terrain (Data from
table 5).
Debris aprons located on the global escarpment and around the 1st tier of the
northern fretted blocks are generally steep (>30%) and small. Farther from the
escarpment to the north, these aprons become more shallow in angle of repose (<30%)
and are much more pronounced and encompass a greater area than the 1st tier blocks
(Fig. 25). Conversely, almost all of the northern low fretted blocks have broad, low angle
aprons that in some places overlap one another. The transition from blocky to knobby
material becomes evident around 100 km from the escarpment.
74
Figure. 25. Mosaic of CTX images composed in Google Earth 5.0: (a) examples of
northern fretted blocks < 50 km from escarpment; (b) examples of northern low fretted
blocks > 200 km from escarpment. Images from Arizona State University, Context
Camera Images (2007 ? 2008).
75
Mineralogically at this scale, mafic material and oxidized iron minerals are the
dominant regime as collected by spectral analysis from CRISM. This material constituted
the individual blocks as well as the valley fill. Geomorphologically the blocks show no
sign of rotation in any direction (x, y, or z) and some blocks have degraded in situ into
multiple blocks. Evidence of fluvial incisions from the southern highlands is found along
the entire escarpment, but their sinuous nature ceases along the boundary line (Fig. 26).
The northern low polygons seem to be associated with multiple impact structures that
dominate the area instead of the northern polygons which follow a fault/fracture pattern.
Figure 26. Sinuous nature of fluid transport along the northern global escarpment.
Modified from USGS MOLA DEM (1999); northern fretted terrain ? beige blocks; red
arrows ? areas of fluid incision.
76
Local Analysis
Local scale involves any section/area that is smaller than 50 km. Major geologic
and geomorphic differences can be seen at this resolution. Geologically, individual
CRISM images show a diverse and constantly changing landscape. While the tops of the
blocks are predominately mafic, in some the lower lying elevations along parts of the
escarpment in the fretted valleys a variety of minerals including iron, iron oxides, olivine,
pyroxene, Fe/Mg phyllosilicates, and clays can be found. In situ weathered rock and
regolith so close in proximity to one another provides evidence of continual mass
transport and altering of sediment in the more recent Martian past (Fig. 27). In regions
greater than 30? latitude, sources of water bound ices can be found as well.
Figure 27. CRISM image 0000AC07 from Google Earth 5.0 showing varied mineralogy
found in the fretted valley regions. Images from Arizona State University, CRISM
Images (2008).
77
Investigation of geomorphology also provides insight into the constantly changing
landscape. Multiple episodes of more recent slumping/mass wasting can be seen on the
flanks of many fretted blocks (Fig. 28; NASA 2010e:PDS).
78
Fig
ure
28.
CR
ISM
im
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s 0008986
and
0009605
showing
mass
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iven
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ess
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ata
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79
Evidence of lineated valley fill is visible in many of the fretted valleys. The current
theories that address the formation of these features are: (1) mobilization of ice-rich
regolith due to sublimation; and (2) glacial moraines (Carr 1996; Fig. 29). Possible
scenarios will be addressed in the discussion section.
80
Figure 29. Example of HiRISE images showing lineated valley fill found between fretted
blocks. HiRISE image 005737 from Arizona State University (2007).
81
INTERPRETATION AND DISCUSSION
Mars is a planet that is encircled by a hemispheric dichotomy that has been dated
using crater counting techniques to be between 4.1 and 3.9 billion years old (Watters et
al. 2007). The northern lowlands comprise roughly 1/3 of the planet?s surface and are on
average 4 km lower in elevation than the southern highlands (Watters et al. 2007). The
crust is about 25 km thicker in the southern highlands and this buoyancy is expressed as
higher elevation topography (Aharonson et al. 2004). The expression of these elevation
differences can be compared to the Earth?s continents and the ocean basins, however
spatial consistency is not found along the entire escarpment that encircles Mars. An
abrupt 1 km vertical change which is dominantly in the form of a steep scarp is located
west of Isidis (280? to 350?) and varies greatly from the same 1 km elevation change in
Arabia Terra region (350? to 30?) which can sprawl for almost 1,000 km horizontally.
Many geologically complex features can also be found along the transition zone between
the southern highlands and the northern lowlands. In the eastern hemisphere, fretted and
knobby terrains (mesas and knolls) are located along the boundary and stretch for 100?s
of km in some areas (Sharp 1973). Endogenic or exogenic processes are the two main
competing hypotheses for the formation of the global escarpment. One of the problems
with testing either of these theories lies in the fact that 30% of the boundary has been
covered by more recent Tharsis volcanism (Andrew-Hanna et al. 2008). Other
assessments involve resurfacing of the northern basin after the formation of the
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dichotomy. These would include either volcanic and/or sedimentary processes that
continue to be active on Mars to the present day.
Endogenic processes
Endogenic or internal processes comprise any mode that involves convection to
some degree that would be driven by heat, pressure, composition, and viscosity - along
with others constituents. These processes invoke no outside sources of energy that would
be considered extraterrestrial in origin. Models are one of the best ways to study and
interpolate these alterations in the early crustal formation history of Mars. The two main
hypotheses that introduce these mechanics are degree-1or long-wavelength mantle
convection and plate tectonics. Remote sensing information gathered by past and current
satellites has added additional data to these theories. The composition of Mars is critical
in the understanding and analysis of these internal processes (Fig. 30).
83
Figure 30. One possible view of the Martian interior. From Stevenson (2001).
Remnant magnetism present in the crust reveal a primitive dynamo that persisted for
approximately 0.5 billion years early in Martian history (Williams and Nimmo 2004).
The presence of an active dynamo and the convection driven in the core can be explained
by two processes. Either the initial Martian core was substantially hotter than the over
lying mantle, due to radioactive decay of K40, U235, U238, and Th 232 and the presence of
sufficient sulfur, or a rapidly cooling mantle due to the size of Mars were the driving
forces behind this heat flux (Williams and Nimmo 2004). If the SNC meteorites are from
84
Mars, then an estimate of 14% sulfur for the core is determined which would allow for a
partially molten core to persist for upwards of 1 billion years (Boyce 2002).
Degree-1 mantle convection
Degree-1 mantle convection models are one way to study and assess large scale,
single hemispheric anomalies (Zuber et al. 2001). The Martian dichotomy and the Tharsis
volcanic rise are two examples of such structures (Harder and Christensen 1996). Past
modeling studies have suggested that there is a viscosity increase in the lower mantle on
Earth (Hager and Richards 1989) so the same approach is used when modeling the early
Martian interior.
Zhong and Zuber (2001) demonstrate that by altering the viscosity of a layered
mantle that long-wavelength patterns are produced using Rayleigh-Taylor instability
analysis and finite element convection models. At the end of planetary accretion process,
a high thermal gradient could be found between the core and mantle producing a low
viscosity layer at the base of the mantle which could lead to a single, hemispheric super
plume (Ke and Solomatov 2006).
There are three scenarios for degree-1 mantle plumes to form the dichotomy. The
first example is directly after the main accretion phase of the planet where no substantial
crust has formed. A single plume forms above the solidus phase and then extruded to
form new crust (Roberts 2004). The second example consists of a stagnant lid with a
uniform >50 km thick crust to form on the planet. An upwelling mantle plume would
erode away or undercut the crust and redeposit the material above the down welling
fringe (Wise et al. 1979ab). Finally the last scenario is a similar combination of the first
two examples. A degree-one mantle plume would cause a thickening of one hemisphere
85
due to upwelling and consequentially producing a thinner opposite hemisphere due to
relaxation of the overlying crust (Zhong and Zuber 2001; Fig. 31).
Figure 31. Example of Rayleigh-Taylor instability analysis with 3 differing viscosities.
Radius to initial boundary is 1,325 km with an 80 km thick lid. From Zhong and Zuber
(2001).
Rock rheology is the driving force for any internal process of a planet. If the
Martian mantle/core boundary is located around the ?-spinel to perovskite boundary, the
time range for a degree-1 convection cell to form exceeds 2 billion years using a finite
element model with an endothermic phase change (Harder and Christensen 1996). Breuer
et al. (1998) used many exothermic phase reactions at the olivine-spinel transition with
lowered pressure and free slip boundary conditions, but with the introduction of
temperature dependant viscosity the age for a single convection plume to form exceeds
4.5 billion years. Clearly there are timing issues with this model since the global
86
escarpment is ~ 4 billion years old. Other models composed by (Roberts and Zhong
2006) show that with a layered mantle, viscosities can differ by >100 times and the
resulting mantle plume can develop on a time scale of 100 million years.
Varying models show that a degree-1 mantle plume can form a hemispheric
dichotomy that is present on Mars today. However many assumptions in composition,
depth, and viscosity have to be inferred. Problems are invoked when we look at the
crustal thickness of Mars (Fig. 32).
Figure 32. Modeled crustal thickness map (0.5 pixel/degree). White line delineates
escarpment boundary line. Image modified from Andrews- Hanna et al. (2008).
The first example for degree-one mantle convection proposes that the entire
southern hemisphere was formed by a single upwelling. As magma was extruded to form
the primordial crust, there should have been a gradual thickening of the crust toward the
center of the plume with a waning in thickness as you move toward the outward extent of
the plume resulting in a lens shape. Clearly there is a distinct difference in crustal
87
thickness as traced by the steepest slope path of the escarpment ranging from 75 to 30 km
thick in just a few 10?s of kilometers contradicting a lenticular shape.
The second example inversely states that the plume scoured or undercut the
northern hemisphere crust and redeposited the material at the edge of the plume. If this
were the case (see Fig. 32), we would expect to see the thickest portion of the crust on the
southern side of the escarpment due to accretion. The fretted terrain could be a remnant
of this condition due to crustal collapse at the escarpment boundary, but does not explain
how these mesas and knobs extend for 100?s of kilometers northward. The fretted blocks
are not tilted toward the northern basin as you would expect if there had been crustal
thinning and collapse along the escarpment.
The last example provides evidence of thickening and thinning of both
hemispheres simultaneously. Extremely high viscosities are needed at the mantle/core
boundary for such a large scale feature to be produced. Although the strong difference in
crustal thickness along the escarpment along with the horizontality of the tops of the
fretted blocks would contradict such an outcome.
Another problem that arises is the fact that any type of degree-1 mantle plume
could not produce such a lengthy, steep, stable cliff like the global escarpment that would
have a life span of more than 4 billion years. Presently there is only one way to produce
such a structure of this magnitude and that is through plate tectonics. Lastly and taking
into account Andrews-Hanna?s model (Fig. 8) of the global escarpment before the
Tharsis rise was present; we can see a distinct elliptical shape which could not be
produced by mantle convection alone (Kiefer 2008). Degree-1 mantle plumes are not
symmetrical and would produce finger-like patterns on the outer fringe which do not
88
match the approximate linear pattern that we see in the crustal thickness of today (see
Fig. 10).
Plate Tectonics
The other endogenic process that could have produced the Martian dichotomy
would be plate tectonics. This ongoing process on Earth creates new crustal material at
spreading centers and subducts older crustal material to maintain isostatic equilibrium
(Fig. 33). Convection processes from the mantle driven by heat loss and the change in
density of the newly formed plate over an extended period time are the driving force
behind plate movement (Bercovici 2003). Plate tectonics is an effective process for
mantle cooling and would help drive an early dynamo (Nimmo and Stevenson 2001).
89
Figure 33. Picture depicting sea floor spreading through time A-D, which produces a
steep terrace. From Scienceray (2010), Great discoveries in the field of Earth science.
(Accessed: 24 May 2010).
On Mars, older, marginal crust would have been subducted, while a process akin
to terrestrial seafloor spreading would have produced the younger northern lowlands in
the early Noachian (Sleep 1994). The expression of this activity would be a relatively
symmetrical crustal thickness across the northern basin with a gradual thickening at the
escarpment boundary with an abrupt change around the subduction zone/continental
margin which is seen in Figure 33. However, there are fallacies in this theory as well.
The northern basin on Mars is approximately 8,500 km wide and 10,600 km long
and covers 40% of the planet?s surface (Andrews-Hanna et al. 2008). Using maximum
spreading rates on Earth, it would take 100?s of millions of years to produce such a basin
90
by this process. Comparison of the density of quasi-circular depressions (QCD)
contradicts this spreading motion (Frey 2004). Mars is smaller than Earth and would have
cooled more rapidly. If plate tectonics were to have happened on Mars, it would have
been brief. It is unclear if mantle convection could cause subduction of a crust 50 km
thick because the basalt-eclogite phase transition does not occur until a depth of ~200 km
(Zuber et al. 2000). Other discrepancies are there is no evidence of any large, relic
subduction zone either along or near the escarpment which would constitute orogenic
morphologies including trenches, mountain chains, or major rifting zones (Watters et al.
2007).
Exogenic processes
External or extraterrestrial processes could have formed the global escarpment.
Excavation and ballistic projection of material due to an impact can form a steep cliff in
the embodiment of a crater wall. At the end of planetary formation, it is estimated that the
inner solar system was populated by ~20 Mars to Moon sized objects (Kominami and Ida
2002). Multiple planetesimals could have shared the same orbit at differing Lagrangian
points similar to the Trojan asteroids located in orbit around Jupiter (Freitas and Valdes
1980). Eventually these orbits become unstable and either a catastrophic collision or
ejection from the inner solar system will occur. The current hypothesis about the Earth-
Moon system is thought to be a collisional event that tilted the Earth?s axis to its present
orientation. The major accretionary process for the inner planets ceased at the end of the
heavy bombardment ~3.8 billion years ago (Gomes et al. 2005). The proximity of Mars
to Jupiter and the asteroid belt make it a likely candidate for a greater density of large
impacts.
91
Multiple impacts
Unlike endogenic processes, impact models do not have a problem with time
constraints. Using crater counting techniques, we know that the global escarpment
predates the end of the heavy bombardment era (Frey and Schultz 1988). Evidence of this
catastrophic event can be seen on all the objects in the inner solar system. The close
proximity of Mars to the asteroid belt and the large gaseous planets made it a prime target
for collisions.
Tracing the transition zone between the southern highlands and the northern
lowlands using topography and crustal thickness models we see the dichotomy is
irregular and not circular in shape lending that a single impact was not the source (Zuber
et al. 2000). Multiple large impacts would provide an alternative answer for the irregular
shape of the northern basin.
Impact craters of considerable size (>200 km) would leave a considerably high
topographic rim compared to the surrounding relief, yet there is no evidence of this in the
northern basin using MOLA data (Fig. 34 a). A good example of one of these structures
is the Utopia basin which is ~3,000 km in diameter, but has no relic crater rim (Fig. 34 b).
For this to be plausible, more than 2 km of sediment would have to fill the entire northern
basin to subdue this topography (McGill and Squyres 1991). Later volcanism has
resurfaced the northern basin in the past, but there is no evidence of a long, sustained era
in which kilometers of flow which is needed to erase impacts of this magnitude.
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3 0 0 0 k m
Figure 34. Topographic and Crustal thickness maps: (a) MOLA relief map, Black line is
traced escarpment; (b) crustal thickness map, Black line is traced escarpment; White
ellipse is Utopia impact site: Black ellipses mark sites of major thinning due to other
impacts. Images were modified from USGS MOLA DEM (1999) and Andrews- Hanna et
al. (2008).
Furthermore, it would take many Utopia scale impacts to account for the amount
of material that is missing from the basin. Not only is it unlikely that a cluster of large
bolides preferentially struck one hemisphere of Mars, but there are no structural features
to affirm this claim. These features would include crater rims, concentric radial fractures,
93
and overlapping ejects blankets (Frey and Schultz 1988). While multiple impacts could
have produced some of the escarpment, crustal thickness maps shed doubt on the scenario
for the total escarpment formation (Fig. 34).
Single impact
Large impacts are common throughout the solar system. Almost any terrestrial
body demonstrates these features including Mercury, Mars, the Moon, and many of
Jupiter?s and Saturn?s moons (see Table 4). The inner solar system was cluttered with at
least 20 Mars- or larger size bodies during the early Noachian era (Kominami and Ida
2002). This provides a basis on which assumptions of mega-impacts can be inferred.
Again, the Earth-Moon theory is thought to be one such impact.
Wilhelm and Squyres (1984) first proposed that a single giant impact could have
formed the northern basin on Mars. Since that time, the shape of a non-circular
corresponding global escarpment has led to question that theory. With a better
understanding of impact events, we now know that impacts can be circular or elliptical
depending on the angle of entry. There are several examples of elliptically shaped impact
basins on Mars and other planets.
Andrews-Hanna et al. (2008) modeled the crustal thicknesses of Mars extracting
the mass of the Tharsis rise to view the dichotomy before its emplacement. By comparing
his results with other accepted elliptical basins found in the solar system, definite
similarities arise (Fig. 35).
94
Figure 35. Comparison of three major elliptical basins: (a) northern polar projection of
Martian topography; (b) modeled crustal thickness of Mars removing the Tharsis rise; (c)
topographic polar projection of the South-Pole Aitken basin on the Moon; (d) the Hellas
basin on Mars. Modified from Google Earth 5.0, USGS MOLA DEM (1999), and
Andrews-Hanna et al. (2008).
The ratios of major to minor axis for these 3 major impacts from figure 35 are: (1)
Borealis basin 10,600/8,500 km = 1.25; (2) South Pole-Aitken basin 2,125/1,542 km =
1.38; and (3) Hellas basin 2,414/1,820 km = 1.33. Any deviance from a true elliptical
shape can be attributed to tectonic activity, later impact overprinting, and/or local erosion
95
(Andrew-Hanna et al. 2008). There are confirmed partial ring structures associated with
the South-Pole Aitken basin and Hellas. With this in mind, the fretted terrain could be a
partial relic ring structure. Timing is not issue with of a single impact as there would be
for any endogenic process. Because the formation of the global escarpment predates the
end of the heavy bombardment, it could have been modified by other later impacts thus a
uniform basin thickness would have been altered as well. With an oblique impact of this
size, the resulting crustal removal would blanket the entire planet and the melt would be
largely contained in the transient crater (Marinova et al. 2008). Since the majority of the
energy would be expelled in the form of ejecta due to a low angle impact, the entire
surface of the planet would not melt and hence leave evidence of such an event (Hart et
al. 2007). Even at an oblique angle of entry, such an impactor should produce a partial
multi-ring structure. Again, a remnant of this could be the fretted terrain that borders the
global escarpment (Fig. 36).
96
4 0 0 k m
3 0 0 k m
Figure 36. MOLA greyscale scale DEM: (a) northern escarpment - light blue line, 50 km
buffers - red and blue lines, fretted terrain - green polygons; and (b) northern low
escarpment - yellow line, 50 km buffers - red and blue dashed line, northern low fretted
terrain - yellow polygons. Modified from USGS MOLA DEM (1999).
97
An impact of this magnitude would have excavated the entire crust from the area thus
exposing mantle material and producing a decompression magma ocean for a period of
time. Mineralogical maps derived from TES show a distinct difference in geology
between the northern lowlands and the southern highlands. The southern highlands are
dominated by basaltic flows, while a higher concentration of andesite is found in the
northern basin (see Fig. 22 a-b). This is easily explained if a mega-impact cleaved out the
initial crust and was then refilled with underlying mantle material As material resurged
into the crater, undercutting of existing crust could have caused a possible rafting effect
similar to iceberg calving transporting cohesive blocks for large distances due to density
variations between the crust and underlying mantle material (Melosh 1989; Fig. 37).
Figure 37. Possible motion of lithosphere and underlying fluidized mantle material during
a major impact. From Melosh (1989).
Defining similarities arise when accessing the data acquired during this project.
Regarding Figure 36 a, there is a continuous fracture line that runs almost the entire
length of the northern escarpment that corresponds to the 50 km buffer zone. All large
blocks trend identically to their position on the escarpment. These larger 1st tier blocks
are also horizontally equal in elevation with the escarpment with no apparent dip in any
98
direction. This division could a possible ancient outer ring structure that would coincide
with an impact of this magnitude. The thinning of the fretted blocks into knobs traveling
northward away from the escarpment would coincide with an inner ring or rings and
would have been tilted due to their proximity to the basin (Fig. 37). These inner rings
would have been more susceptible to erosional smoothing with the inner peaks rounding
over time and potentially filling in the face of the inward facing scarp.
Another possible outcome for an impact of this magnitude would be a large
deviance of obliquity in the axis of the planet as compared to the orbital stellar plane. As
the large gas giants settled into more stable orbits, some of the remaining inner planets
would have been perturbed out of their orbits. These future projectiles could have struck
multiple planets including the Earth, Mars, and Neptune which would explain their
current axial tilt (Rubin 2002). Mars currently has an axial tilt of ~25?, but it can vary
from 18? to 48? over time (Head et al. 2003). One possible mechanism for this large
variance would be some time in the early history of Mars, a giant impactor struck the
planet, thus tilting its axis and producing such an extreme wobble (Rubin 2002).
Formation and evolution of the fretted terrain
The fretted terrain is the boundary transition zone between the northern lowlands
and the southern highlands. It was recognized to cover 3% of the Martian surface and is a
product of erosive/abstractive processes (Sharp 1973). The terrain is marked by steep,
flat-floor chasms that dissect the blocks which become less abundant the further you
travel from the escarpment (Lucchitta 1984). These fretted blocks which resemble mesas
and buttes on Earth transition into knobs and knolls northward from the escarpment
boundary. The fretted terrain can be found between 280? and 350? longitude plus 25? and
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50? latitude (see Fig. 11). Due to the geographic nature of these blocks, two distinct
regions were used to assess the nature of the formations. They are (1) the northern fretted
terrain- 280? to 325? longitude and 25? to 50? latitude and (2) the northern low fretted
terrain- 325? to 350? longitude and 40? to 50? latitude (Fig. 38).
4 0 0 k m
Figure 38. MOLA greyscale scale DEM showing two regions of escarpment and fretted
terrain (blue line - northern escarpment, green polygons - northern fretted terrain, yellow
line - northern low escarpment, yellow polygons - northern low fretted terrain). Modified
from USGS MOLA DEM (1999).
The formation of the escarpment would have a direct impact as to how the fretted terrain
came to be and was then altered by later processes. If endogenic processes were to have
formed the escarpment problems arise with the current location of some of the blocks and
the amount of material that has been removed. Squyres (1978) notes that the debris
aprons currently found around individual blocks would only account for ~5 km of scarp
retreat, yet we see mesas and knobs more than 300 km from the scarp today. One way to
100
account for these island-like mesas and knobs would be a mega-impact followed by
crustal extension, potential terrace formation, and rafting (Fig. 39).
Figure 39. Possible cohesive, rafted fretted blocks of same elevation located at least 150
km from the global escarpment. Black line ? global escarpment; beige blocks ? northern
fretted terrain blocks; red dashed circles ? possible rafted blocks. Modified from USGS
MOLA DEM (1999).
Associated with the impact, crustal extension in the form of horst and grabens and a tilted
terrace structure could form (Melosh 1989; see Fig. 37). This would greatly reduce the
amount of erosion and sediment transport that would have occurred under normal
conditions and could account for the >300 km distance that is related to some mesas and
knobs. The orientation of the long axis of the northern fretted terrain blocks
approximately parallels the escarpment and the ratio of the long vs. short axis provide
evidence of contiguous extension over a large area (Fig. 40). The 1st tier of the northern
fretted terrain is also horizontally equivalent to the escarpment and shows no preferential
tilt (Fig. 40).
101
a.
1 0 0 k m
Figure 40. Orientation and elevation of the fretted terrain: (a) orientation of fretted blocks
with center of mass, long, and short axes; (b) reclassification of MOLA DEM showing
consistent elevations. Modified from USGS MOLA DEM (1999).
102
The northern low fretted terrain does not show any corresponding trend, but major
overprinting of later impacts could have obliterated any evidence of earlier extensional
fracturing. Crustal contraction of a magma pool during cooling could be formed in a
crater of considerable size. This radial pattern is seen in many crater basins on Mars
including the ones associated with the northern low fretted blocks. A safe assumption on
the lines of this evidence would be that the northern low fretted terrains are the remnants
of later impacts and the majority of the fretted blocks are potentially crater rims and/or
contractional blocks (Fig. 41).
Figure 41. Sections of the global escarpment composed from MOLA-based DEM: (a)
northern section (black line - northern global escarpment, red polygons - northern fretted
blocks, black dots - center of mass of polygon, and white lines- long and short axis); (b)
northern low section (black line - northern low escarpment, white polygons - northern
low fretted blocks, red circles - post escarpment formation impact sites). Modified from
USGS MOLA DEM (1999).
103
Erosional processes have played a major role in the evolution of the fretted
terrain. Many geomorphic processes have been identified on Mars and the timing and
intensity of some of these modifications are debatable. The Martian history is
complicated so differing processes will be addressed separately depending on their place
in history.
After the formation of the escarpment more than 4 billion years ago, Mars would
have been cool enough have a primitive, denser atmosphere. If this were the case, then
water would have been stable at the surface unlike today. Oceans or seas could have
formed in the low lying areas or basins. The extremely flat lying topography which is
located in the northern basin could be attributed to an ancient ocean. To assess the
erosional capability of a potential oceanic shoreline in the northern basin, four different
proposed paleoshores were incorporated in ArcGIS (Fig. 42).
104
a.
1
0
0
k
m
Figure
42. (
a) Re
classifie
d MOLA
-ba
sed
DEM of
pr
opose
d a
nc
ient hi
gh st
and shore
line
s:
northe
rn
low
esc
arpm
ent ar
ea (
bla
ck d
ashed
line
- northe
rn
low
esc
arpm
ent, re
d polygon
s -
northe
rn
low f
rett
ed b
locks)
.
Modi
fie
d fr
om US
GS M
OLA
DEM (
1999)
.
105
b.
1
0
0
k
m
Figure
42. (
b) R
eclassifie
d MOLA
-ba
sed
DEM of
pr
opose
d a
nc
ient hi
gh st
and shore
line
s:
northe
rn
esc
arpm
ent ar
ea (
da
shed
red li
ne
- northe
rn
esc
arp
ment;
Nor
ther
n polygons
are
outl
ined in blac
k). Modif
ied
from US
GS M
OLA
DE
M (1999)
.
106
The four proposed shoreline elevations were extracted using MOLA data with imagery
and correspond to possible high stands. These elevations are -1,680 m and -3,760 m from
Head et al. (1999) along with -3,509 m and -4,350 m from Baker et al. (1991). Analyzing
these four proposed shorelines some fallacies become apparent. In the northern fretted
terrain only the -1,680 m elevation would have been able to gradually erode the
escarpment. Again Squyres (1978) attributes only ~5 km of retreat over the life of the
escarpment providing question as to the northern fretted terrains being formed only due
to erosional processes of a potential shoreline. Of the four shorelines, this elevation is the
most erratic and less contiguous over long distances and has a greater tendency for
topographic modification over time. Due to the lower elevations present in the northern
low escarpment region alterations are far more likely with any of the four paleoshoreline
elevations with complete submergence at the -1,680 m line. Erosional processes could
have contributed to mass wasting and larger debris aprons that are seen around the
northern low fretted blocks. The point of this analysis is not to justify the presence of a
past ocean, but simply to show possible analogs that would correspond with these ancient
shorelines.
Findings using analysis on recently studied craters and by the Pathfinder Rover
show strong evidence that subsurface ice is stable on Mars at relatively shallow depths
(Smith et al. 2009). One example of this is CRISM image 0009DEC (Fig. 43). Looking
closely at the sediment transport pattern, we can deduce that liquid water has possibly
breached the crater rim and flown down gradient. Also the non interconnecting rill
pattern seen on the side of the block lends to more recent activity possibly associated
with the corresponding impact.
107
Figure 43. CRISM image 0009DEC. Recent crater showing reactivation of subsurface
ice by melting. Image from Arizona State University, CRISM database (2006).
Due to these confirmations, the scarp recession by the undermining of an overlying
resistant material in the form of weathering is a viable solution to the transport
mechanisms that form the fretted terrain (Sharp 1973). Outlying mesa and buttes of the
region are irregular in shape and lack a streamline appearance that would more resemble
fluvial transport (Lucchitta 1984). These fretted blocks are also non-uniform in shape,
while on Earth such formations tend to be aligned parallel or become conical in varying
108
wind patterns (Breed et al. 1982). The extent as to when this process began is still
debatable, but is an ongoing process today that could been accelerated in the recent past
by Milankovitch-type cycles.
Milankovitch?s proposal that the Earth?s climate has been modulated through time
due to changes in the axial tilt and other orbital parameters is well accepted in the
scientific community today (Short et al. 1991). These three cycles on Mars are: (1)
eccentricity ? the change in shape of Mars? orbit around the Sun; (2) precession - the
slow wobble as it spins on axis; and (3) obliquity - the inclination of Mars? axis in
relation to its plane of orbit around the Sun are thought to be the cause of glacial periods
on Mars in the past (Fig. 44).
109
Figure 44. Insolation, eccentricity, and obliquity of Martian polar region over two time
scales. From Lasker (2002).
110
The eccentricity of the Martian orbit ranges from 0.004 to 0.141 (0 to 14%) and
today is currently at 0.093. This change in shape is interwoven into a 95 to 99 k.y. cycle
with a longer 2.4 m.y. resonance (Ward 1974). Precession of Mars constitutes a cycle of
175 k.y. years (Head et al. 2003). The Martian obliquity cycle is 120 k.y. with a longer
1.2 m.y. resonance. The present obliquity is 25? and has a rather wide range of 18? to 48?
compared to the smaller change of 21.5? to 24.5? for the Earth. Obliquity is the most
important of the three cycles because it directly determines the amount of sunlight that
reaches the poles. Periods of high obliquity correspond with removal of ice at the polar
cap and redeposition at lower latitudes (Phillips et al. 2008). This period - referred to as
an ?ice age? - would result in a possible buildup of dust/sediment in the polar region
(Fig. 45).
111
Figure 45. Movement of ices on the Martian surface through time. Modified from
Sch?rghofer (2007).
The continued fluctuations in the Martian seasons and obliquity can cause massive
transport of ice from polar to lower latitudes or inversely from lower latitudes to the polar
region. The additional accretion of interbedded ice and soil followed by the sublimation
112
of ices would give rise a constantly changing landscape. Evidence of this process can be
seen in the northern fretted region. Possible glacial evidence may be present in the form
of moraines (Fig. 46).
Figure 46 a. Wide field view of CTX image P01_001570_2213_XI_41N305W in Google
Earth with possible ice induced movement highlighted in red circles. Image from Arizona
State University, Context images (2006).
113
Figure 46 b. Overhead close up view of CTX image P01_001570_2213_XI_41N305W
in Google Earth with possible end moraines at margin of a fretted block. Image from
Arizona State University, Context images (2006).
114
Figure 46 c. Cirque-like feature with end moraines viewed at 60?from horizontal in
Google Earth. Vertical exaggeration 3:1. Image from Arizona State University, Context
images (2006).
It is important to note that there is no evidence of these features found south of 30?. More
recent sublimation activity can be seen in the northern low fretted terrain. With the
abundance of ice found in the vicinity of the surface, it may be safe to assume that some
type of cryogenic karst modification would be present. An example of this can be found
in the form of ice wedge polygons which resemble Earth-like features found in arctic
regions (see Figs. 13 and 47).
115
Figure 47. HiRISE image PSP_005738_2245RED showing possible cryogenic karst
alteration found in the northern low fretted terrain. Image from Arizona State University,
HiRISE database (2007).
116
CONCLUSION AND FURTHER WORK
Investigations show that Mars has been tectonically and hydrologically active
throughout the past 4.5 billion years. Of all the planets, Martian geomorphology bears the
closest resemblance to what we see on Earth. Whether the global escarpment was formed
by internal or external force does not change the fact that it is one of the most impressive
structures found in the solar system.
Discrepancies arise with any of the processes thought to have formed the Martian
dichotomy. While advanced modeling techniques using internal heat flow have helped
address some of the mega-features on the Martian surface, many assumptions have to be
considered in assessing the outcome of these models. Early in the formation of Mars,
energy in the interior would have been sufficient enough to cause a degree-1 mantle
plume. Troubles emerge with the initial cooling rate of the planet to form a stagnant lid of
sufficient thickness and incorporation of a mantle/core boundary with viscosity deviance
greater than 100 fold. Plate tectonics can explain many observations, but the lack of a
relic subduction zone and no mountain chains along the escarpment provide problems
with this theory as well. Multiple impacts can account for the irregular shape of the
escarpment, but crustal thickness models and the biased assumption of many large
impacts in a single hemisphere is unlikely. With the research and data acquired during
this project, a single mega-impact can answer most of the underlying questions about the
escarpment and account for the fretted terrain as a consequence. The shape of the
117
Borealis basin is not circular/elliptical today but, models extracting the Tharsis rise and
more than 4 billion years of modification can more than account these irregularities. The
northern fretted terrain may be the possible remnant of a ring structure and could account
for much of the apparent material loss for the region due to crustal contraction. The
northern low fretted terrain is most likely contractional blocks and younger, smaller
crater rims. The two fretted terrain regions have both been modified by both fluvial and
aeolian processes in the past, but the transport of material by the fretting process is the
dominant regime of geomorphologic change today. The examination of data in this paper
tends to encourage the single impact theory as the most plausible outcome for the
formation of the global escarpment and fretted terrain. This does not rule out any of the
other postulated theories, but sheds insight into further investigation on the matter.
Further work would be invaluable in confining the formational and evolutional
processes of the Martian dichotomy. The release of new images can provide more data
for analysis. The SHARAD imagery database of ground penetrating radar would also
help in interpretations of the shallow subsurface. New and improved modeling techniques
can help explain the internal workings of a planet the size of Mars.
118
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127
APPENDIX
ArcMap 9.2
Application Source
Retrieve missing right click on file>>repair source>>file
File (!)
Checking application click on view>>tool bar or right click on file
Insertion
Georeferencing add data, then select data>>right click>>zoom to layer
(set layer that will be referenced 1st in the appropriate tool bar)
then click and add control points
Updating
Georeferenced map click on georeference drop down>>update georeferencing
Transparency right click on layer>>display>>change transparency
Source for a click on source at bottom of map layers box
Particular layer
Creating a new click on view>>data frame properties>>coordinate
Coordinate system system>>new>>projected coordinate system>>Mars 2000
Changing color right click on layer>>properties>>symbology>>color ramp
On an existing map
Attributes table right click on layer>>open attributes table
Reclassification right click on layer>>symbology>>classified>>select number
of classes or
arc tool box>>spatial analyst tools>>surface>>reclassify or
arc tool box>>3D analyst tools>> raster reclass
Saving layers right click on layer>>save layer as
Saving maps file>>save map
128
Slope arc tool box>>spatial analyst tools>>surface>>slope or
click on 3D analyst>>surface analysis>>slope
Aspect arc tool box>>spatial analyst tools>>surface>>aspect or
click on 3D analyst>>surface analysis>>aspect
Contour lines arc tool box>>spatial analyst tools>>surface>>contour or
click on 3D analyst>>surface analysis>>contour
Interpolation arc tool box>>spatial analyst tools>>surface>>kringing
Clipping an arc tool box>>analysis tools>>extract>>clip
image
Intersecting arc tool box>>analysis tools>>overlay>>intersect
two items
Union of arc tool box>>analysis tools>>overlay>>union
Two items
Buffering arc tool box>>analysis tools>>proximity>>buffer
Selecting click on the select feature tool>>then click on feature
a feature
Identifying click on the identify feature tool>>them click on feature
a feature
Creating
Topographic profiles click on 3D analyst>>surface analysis>>contour
then right click on interpolate line tool, draw line
click on profile graph to open cross section
Exporting tables file>>right click>>attribute table>>export>>text file
when opening in excel you must change the comma
to a column for file to be read
Exporting cross right click on line>>right click on profile>>export>>save as a
sections jpeg
Adding fields to file>>right click>>attribute table>>options>>add field
attribute tables
Adding tools file>>right click>>attribute table>>right click on field
calculator>>left click load>>tool
129
ArcCatalog 9.2
Application Source
Creating a right click on contents>>new>>personal geodatabase>>double
geodatabase click to open
Creating feature right click on contents>>new>>feature data set
data set
Creating feature right click on contents>>new>>feature class
class
Exporting tables right click on layer>>attributes>>export
130
List of images addressed in this project.
CTX
P02_001844_1738_XN_06S214W- P02_001831_1768_XN_03S220W
P02_001857_1750_XN_05S209W- P02_001847_2152_XN_35N302W
P02_001989_1756_XN_04S213W- P02_001923_1746_XN_05S211W
P03_002112_2208_XN_40N337W- P03_002032_2220_XN_42N313W
P03_002138_2194_XN_39N327W- P03_002135_1861_XN_06N241W
P04_002635_1727_XN_07S210W- P03_002345_1759_XI_04S213W
P05_002886_1798_XN_00S223W- P04_002717_2128_XN_32N293W
P05_002913_1859_XN_05N241W- P05_002899_1759_XI_04S218W
P06_003310_2082_XI_28N282W- P05_002925_1730_XN_07S207W
P06_003479_1745_XN_05S212W- P06_003466_1757_XI_04S217W
P07_003624_1726_XN_07S210W- P07_003585_1772_XN_02S226W
P07_003704_1825_XN_02N235W- P07_003651_1763_XN_03S228W
P07_003835_1736_XN_06S211W- P07_003769_1742_XN_05S209W
P08_004218_1748_XI_05S227W- P08_003980_1727_XI_07S210W
P10_005062_1794_XN_00S230W- P09_004693_1820_XN_02N236W
P11_005247_1885_XN_08N242W- P10_005115_1821_XN_02N237W
P11_005378_1755_XN_04S217W- P11_005273_1814_XN_01N231W
P11_005407_2129_XN_32N293W- P11_005392_1879_XN_07N240W
P11_005460_2151_XI_35N300W- P11_005420_2108_XI_30N287W
P12_005697_2134_XI_33N291W- P12_005615_1742_XI_05S207W
P13_005946_1888_XN_08N245W- P12_005787_1779_XN_02S223W
P13_006160_2252_XN_45N334W- P13_006157_1906_XN_10N247W
P13_006198_2095_XN_29N289W- P13_006185_2116_XN_31N294W
P13_006223_1919_XN_11N249W- P13_006199_2245_XN_44N318W
P13_006238_2219_XN_41N303W- P13_006236_1892_XN_09N244W
P13_006252_2208_XN_40N325W- P13_006249_1841_XN_04N238W
P13_006264_2147_XN_34N292W- P13_006262_1824_XN_02N233W
P13_006278_2246_XN_44N315W- P13_006265_2271_XN_47N321W
P13_006288_1785_XN_01S222W- P13_006279_2234_XN_43N342W
P13_006290_2056_XN_25N280W- P13_006289_1919_XN_11N251W
P14_006473_1823_XI_02N234W- P14_006460_1859_XN_05N239W
P14_006582_2214_XN_41N335W- P14_006475_2149_XN_34N293W
P14_006635_2267_XN_46N343W- P14_006595_2269_XN_46N331W
P14_006660_2233_XN_43N305W- P14_006658_1895_XN_09N246W
P15_006713_2212_XN_41N312W- P14_006699_2135_XN_33N288W
P15_006724_1908_XN_10N248W- P15_006714_2256_XI_45N340W
P15_006737_1901_XN_10N243W- P15_006726_2245_XN_44N307W
P15_006858_2226_XN_42N311W- P15_006806_2202_XN_40N330W
P15_006925_2229_XN_42N340W- P15_006885_2269_XN_46N329W
P15_006961_1823_XN_02N238W- P15_006937_2222_XN_42N308W
P15_006989_2137_XN_33N287W- P15_006974_1862_XN_06N233W
131
P15_007003_2246_XN_44N310W- P15_007002_2107_XN_30N281W
P15_007040_1818_XI_01N234W- P15_007082_2245_XN_44N308W
P16_007132_1766_XN_03S226W- P16_007145_1783_XN_01S221W
P16_007161_2209_XN_40N304W- P16_007162_2263_XN_46N332W
P16_007174_2154_XN_35N299W- P16_007198_1805_XN_00N229W
P16_007201_2257_XN_45N316W- P16_007213_2065_XN_26N282W
P16_007214_2257_XN_45N312W- P16_007215_2254_XN_45N339W
P16_007359_2220_XN_42N311W- P16_007360_2244_XN_44N338W
P16_007372_2232_XN_43N306W- P16_007383_1897_XN_09N242W
P16_007385_2149_XN_34N300W- P16_007396_1826_XN_02N236W
P16_007398_2166_XN_36N295W- P16_007425_2220_XN_42N313W
P16_007426_2266_XN_46N341W- P16_007464_2124_XN_32N296W
P17_007490_2095_XN_29N286W- P17_007514_1755_XN_04S217W
P17_007530_2149_XN_34N299W- P17_007541_1822_XN_02N235W
P17_007543_2162_XN_36N294W- P17_007569_2143_XN_34N284W
P17_007557_2256_XN_45N318W- P17_007581_1911_XN_11N248W
P17_007571_2200_XN_40N340W- P17_007593_1739_XN_06S214W
P17_007583_2216_XN_41N307W- P17_007676_2208_XN_40N327W
P17_007623_2271_XI_47N320W- P17_007701_2091_XN_29N287W
P17_007689_2259_XI_45N322W- P17_007715_2232_XN_43N312W
P17_007702_2245_XN_44N317W- P17_007725_1765_XN_03S219W
P17_007716_2203_XN_40N339W- P17_007729_2250_XN_45N334W
P17_007728_2207_XN_40N306W- P17_007742_2239_XI_43N329W
P17_007738_1759_XN_04S214W- P17_007752_1832_XN_03N237W
P17_007751_1710_XN_09S209W- P17_007781_2256_XN_45N314W
P17_007755_2249_XN_44N324W- P17_007808_2210_XN_41N331W
P17_007782_2219_XN_41N341W- P17_007861_2192_XN_39N338W
P17_007831_1787_XI_01S233W- P18_007900_2237_XN_43N324W
P17_007873_2242_XN_44N306W- P18_007913_2244_XN_44N319W
P18_007912_2142_XN_34N290W- P18_008068_1757_XN_04S225W
P18_007979_2264_XN_46N321W- P18_008173_1736_XI_06S211W
P18_008085_2256_XN_45N335W- P19_008266_1793_XI_00S232W
P18_008243_2219_XI_41N329W- P19_008309_2265_XI_46N332W
P19_008292_1746_XI_05S220W- P19_008533_2261_XI_46N330W
P19_008441_2247_XN_44N337W- P19_008545_2123_XI_32N295W
P19_008542_1710_XN_09S208W- P20_008714_1791_XN_00S226W
P19_008573_2263_XI_46N342W- P20_008743_2173_XN_37N303W
P20_008731_2218_XN_41N336W- P20_008912_1821_XN_02N233W
P20_008902_2209_XN_40N325W- P21_009281_1762_XN_03S227W
P21_009087_2196_XN_39N336W- P22_009611_1823_XN_02N237W
P22_009584_1746_XI_05S220W- P22_009652_2099_XN_29N280W
P22_009639_2114_XN_31N285W- P22_009799_2205_XN_40N336W
P22_009653_2224_XN_42N309W-
132
CRISM
FRT0000AA76_07_IF167L_IRA1 FRT0000AA76_07_IF167S_TRU1
FRT0000A81C_07_IF167L_IRA1 FRT0000A81C_07_IF167S_TRU1
FRT0000AD27_07_IF167L_IRA1 FRT0000AD27_07_IF167L_MAF1
FRT0000AD27_07_IF167S_TRU1 FRT0000BCE2_07_IF166L_IRA1
FRT0000BCE2_07_IF166L_PHY1 FRT0000BCE2_07_IF166S_TRU1
FRT00009A07_07_IF167L_IRA1 FRT00009A07_07_IF167S_TRU1
FRT000099C1_07_IF167L_IRA1 FRT000099C1_07_IF167S_TRU1
HRL0000B1B8_07_IF184L_IRA1 HRL0000B1B8_07_IF184S_TRU1
FRT0000A0D8_07_IF164L_MAF1 FRT0000A0D8_07_IF164S_TRU1
FRT0000A10D_07_IF165L_MAF1 FRT0000A10D_07_IF165S_TRU1
FRT0000A26C_07_IF167L_MAF1 FRT0000A26C_07_IF167S_TRU1
FRT0000A53E_07_IF165L_MAF1 FRT0000A53E_07_IF165S_TRU1
FRT0000A230_07_IF167L_MAF1 FRT0000A230_07_IF167S_TRU1
FRT0000AD16_07_IF165L_MAF1 FRT0000AD16_07_IF165S_TRU1
FRT0000B2BE_07_IF165L_MAF1 FRT0000B2BE_07_IF165S_FEM1
FRT0000B2BE_07_IF165S_TRU1 FRT00005DBD_07_IF166L_HYD1
FRT00005DBD_07_IF166L_PHY1 FRT00005DBD_07_IF166S_FEM1
FRT00005DBD_07_IF166S_TRU1 FRT00007FCC_07_IF164L_MAF1
FRT00007FCC_07_IF164S_TRU1 FRT00009B3D_07_IF165L_MAF1
FRT00009B3D_07_IF165S_TRU1 FRT00009BF7_07_IF166L_MAF1
FRT00009BF7_07_IF166S_TRU1 FRT00009DA4_07_IF167L_MAF1
FRT00009DA4_07_IF167S_TRU1 FRT00009DD6_07_IF165L_MAF1
FRT00009DD6_07_IF165S_TRU1 FRT00009DEC_07_IF167L_MAF1
FRT00009DEC_07_IF167S_TRU1 FRT000049FF_07_IF167L_MAF1
FRT000049FF_07_IF167S_FEM1 FRT000049FF_07_IF167S_TRU1
FRT000060A3_07_IF164L_MAF1 FRT000060A3_07_IF164S_TRU1
FRT000063A8_07_IF165L_MAF1 FRT000063A8_07_IF165S_FEM1
FRT000063A8_07_IF165S_TRU1 FRT000080ED_07_IF165L_MAF1
FRT000080ED_07_IF165S_TRU1 FRT0000887C_07_IF167L_MAF1
FRT0000887C_07_IF167S_TRU1 FRT0000952C_07_IF165L_MAF1
FRT0000952C_07_IF165S_TRU1 FRT00005840_07_IF165L_MAF1
FRT00005840_07_IF165S_TRU1 FRT00005905_07_IF165L_MAF1
FRT00005905_07_IF165S_TRU1 FRT00008986_07_IF167L_HYD1
FRT00008986_07_IF167L_MAF1 FRT00008986_07_IF167S_FEM1
FRT00008986_07_IF167S_TRU1 FRT00009213_07_IF167L_MAF1
FRT00009213_07_IF167S_TRU1 FRT00009486_07_IF167L_MAF1
FRT00009486_07_IF167S_TRU1 FRT00009605_07_IF167L_MAF1
FRT00009605_07_IF167S_TRU1 FRT00009652_07_IF165L_MAF1
HRL0000AC07_07_IF183S_FEM1 HRL0000AC07_07_IF183L_PHY1
HRL0000AC07_07_IF183L_MAF1 HRL0000AC07_07_IF183L_HYD1
HRL0000A8EC_07_IF183S_TRU1 HRL0000A8EC_07_IF183S_FEM1
HRL0000A8EC_07_IF183L_PHY1 HRL0000A8EC_07_IF183L_MAF1
HRL0000A8EC_07_IF183L_HYD1 HRL0000A5EA_07_IF184S_TRU1
HRL0000A5EA_07_IF184L_MAF1 FRT00009652_07_IF165S_TRU1
133
HRL0000AC07_07_IF183S_TRU1 HRL0000B29B_07_IF184L_MAF1
HRL0000B29B_07_IF184S_TRU1 HRL0000BEF4_07_IF184L_MAF1
HRL0000BEF4_07_IF184S_TRU1 HRL00009BC1_07_IF181S_TRU1
HRL00009C2A_07_IF182L_MAF1 HRL00009C2A_07_IF182S_TRU1
HRL00002852_07_IF183L_MAF1 HRL00002852_07_IF183S_TRU1
HRL00006408_07_IF183L_HYD1 HRL00006408_07_IF183L_MAF1
HRL00006408_07_IF183L_PHY1 HRL00006408_07_IF183S_FEM1
HRL00006408_07_IF183S_TRU1 HRS0000AC76_07_IF174L_MAF1
HRS0000AC76_07_IF174S_TRU1 HRS00004A28_07_IF174L_MAF1
HRS00004A28_07_IF174S_TRU1 HRS00004130_07_IF176L_MAF1
HRS00004130_07_IF176S_TRU1 HRL0000BF50_07_IF185L_IRA1
HRL0000BF50_07_IF185S_TRU1 HRS0000AB71_07_IF176S_TRU1
HRS0000AB71_07_IF176L_IRA1 HRS0000AB6E_07_IF176L_IRA1
HRS0000AB6E_07_IF176S_TRU1 HRS00004130_07_IF176L_IRA1
HRS00004130_07_IF176S_TRU1
MOC
E0400822 E0101704
E0102224 E0200611
E0300614 E0400806
E0500922 E0503373
E0600246 E1000163
E1000302 E1004234
E1100381 E1103458
E1103584 E1104301
E1200557 E1201400
E1201645 E1400813
E1401008 E1501662
E1900085 E1900278
M0803907 R0502519
R1701197 S0200044
S0901040 S1201657
S1402845 S1500446
E0400822 E0902578
E1000765 E1100398
E1600085 E1800777
R0901181 R1301892
S0301332 S1901131
134
HiRISE
PSP_007424_2080_RED_abrowse PSP_003694_2205_RED_abrowse
PSP_005738_2245_RED_abrowse PSP_005857_2225_RED_abrowse
PSP_006147_2250_RED_abrowse PSP_007096_2215_RED_abrowse
PSP_007215_2255_RED_abrowse PSP_007360_2245_RED_abrowse
PSP_007834_2250_RED_abrowse PSP_008598_2155_RED_thumb
PSP_009733_2240_RED_abrowse PSP_001570_2215_RED_thumb
PSP_005737_2185_RED_abrowse PSP_005843_2260_RED_abrowse
PSP_006251_2125_RED_abrowse PSP_007082_2245_RED_abrowse
PSP_007451_2225_RED_abrowse PSP_007531_2195_RED_abrowse
PSP_007781_2255_RED_abrowse PSP_008190_2255_RED_abrowse
PSP_008611_2125_RED_abrowse PSP_008810_2225_RED_abrowse
PSP_009020_2210_RED_abrowse PSP_009363_2240_RED_abrowse
PSP_009455_2215_RED_abrowse PSP_009719_2230_RED_abrowse