ASTR 121, O'CONNELL. MARS IMAGES
ASTR 121 (O'CONNELL)
SELECTED MARS IMAGES
Mars features the most interesting surface of any planet other than
Earth. Even though Mars is a smaller planet, its land area is about
the same as Earth's (since two-thirds of Earth's surface is covered by
oceans). Mars' terrain is an exaggerated version of the Earth's. The
spacecraft campaign which began in the mid-1990's and will continue
through this decade will yield an enormous amount of information on
Mars.
You can find a large number of beautiful Mars images taken by
terrestrial telescopes and spacecraft on the Web. Some of the better
sites are linked to the
Study Guide 16 page on Mars.
Here, I've selected images which illustrate the variety of terrain on Mars
and the extent to which we are now able to study it from spacecraft.
MOLA Maps of Mars
Topographic maps produced by the Mars Orbiter Laser Altimeter (MOLA)
on the Mars Global Surveyor (MGS) mission (1998-2006). Left: Tharsis
hemisphere. Right: Hellas hemisphere. Color coding is for altitude
(blue is lowest, red high, white is highest---but doesn't indicate
snow). Click on the images for larger versions. For a high-resolution
enlargement, click here.
Identifications for the various Martian features visible here are
given here (main areas)
and here (details).
The Tharsis hemisphere is dominated by the "Tharsis Bulge" a huge surface
deformation which produced striking volcanoes and canyons. The Hellas
hemisphere consists mainly of cratered highlands, punctuated by a
single enormous impact basin (Hellas). The cratering density shows
that the Tharsis hemisphere is significantly younger, on average, than
the Hellas hemisphere. Tharsis is probably 2-3 billion years old.
An even more remarkable asymmetry revealed by the MOLA altitude maps is
the large 5 km (16,500 ft) difference between the mean elevations of
the (low) northern hemisphere and the (high) southern hemisphere. The
north is less heavily cratered (meaning younger) and smoother. It is
dominated by a huge, flat depression (blue in the images above), which
may be the bed of an ancient ocean.
[Source: MOLA Team]
Map of Tharsis
MOLA map of the dramatic Tharsis (left) and Chryse (right) regions on Mars.
Clearly marked are the major Tharsis volcanoes: Olympus Mons (18N,
228E), Alba Patera (40N, 250E) and the volcanic chain consisting of
Ascraeus, Pavonis and Arsia montes. Olympus Mons is the isolated peak
off to the west. In the lower center of the map is the gigantic
Valles Marineris canyon system (stretching from 265E to 310E). At the
right side are the Chryse channels. The large red blotch corresponds
to the "Tharsis Bulge." [Source:
MOLA Team]
Volcano Olympus Mons
Olympus Mons, located west of the Tharsis bulge, is the largest volcano
known in the Solar System, with an altitude of 88,000 feet
(compare to
Mt. Everest at 29,000 ft above sea level and 43,000 ft above the ocean
floor), a diameter of 340 miles, a caldera 44
miles in diameter and flanking cliffs reaching 20,000 feet in
altitude. If situated in Virginia, it would occupy most of the land
area of the state. It is a shield volcano, like the large volcanos in
Hawaii. These tend to have relatively quiescent eruptions of fluid
lava, without the explosiveness associated with ash eruptions or more
viscous lava (as in Mt. St. Helens). The massive concentration of
magma which built up Olympus Mons and the Tharsis bulge apparently
originated in an enormous mantle plume.
This is a composite of Viking images, projected in perspective as if
seen from an altitude of about 30 miles at a distance of about 1500
miles.
Here is a mosaic looking straight down on Olympus Mons.
Caldera of Olympus Mons (Viking)
Volcano Apollinaris Patera
This view of Apollinaris Patera, shows characteristics
of an explosive origin and an effusive origin. Incised valleys in most
of the flanks of Apollinaris Patera indicate ash deposits and an
explosive origin. On the west side (bottom), landslides that have shaped
its surface also indicate ash deposits. Towards the south flank, a
large fan of material flowed out of the volcano. This indicates an
effusive origin. Perhaps during its early development Apollinaris
Patera had an explosive origin with effusive eruptions taking place
later on. [Image & caption by Calvin J. Hamilton.]
Ceraunius Tholus
A Viking vertical view of Ceraunius Tholus, a "small" volcano in the
Tharsis Bulge just north of the three large Tharsis volcanos described
above. Ceraunius is about
21000 feet high; the crater at the summit is about 15 miles across.
The true base of the volcano is submerged in the flood of lava which
produced the surrounding Tharsis plain. Gigantic stress fractures caused by
the upwelling of magma from below
cross this region. Click the image for a much enlarged view.
MGS Image of Elysium Mons
Caldera of Elysium Mons photographed by Mars Global Surveyor with its
narrow angle, high resolution camera (July 1998). This volcano is
41,000 feet high and has a large, round caldera with steep cliffs on
one side. Several channels carved by lava flows are present, but
there is no evidence of erosion by rainfall. Some of the craters are
of impact origin, but most are probably produced by volcanic
activity. About 1/3 of the full MGS image is shown here. Click on
the image for a higher resolution version (272K). The full resolution
of the MGS camera is 17.2 feet per pixel. Click here for an extract at full
resolution of the image near the southern (right side) caldera wall of
the volcano. [Image by Malin Space Science Systems.]
Tharsis Plume Computer Simulation
This image shows a computer simulation of processes
in the interior of Mars that could have produced the Tharsis region.
The color differences are variations in temperature. Hot regions are
red and cold regions are blue and green, with the difference between
the hot and cold regions being as much as 1000 C (1800 F). Because of
thermal expansion, hot rock has a lower density than cold rock. These
differences in density cause the hot material to rise toward the
surface and the cold material to sink into the interior, creating a
large-scale circulation known as mantle convection. This type of
mantle flow produces plate tectonics on Earth.
The hot, rising material tends to push the surface of the planet up,
and the cold, sinking material tends to pull the surface down. These
motions contribute to the overall topography of the planet. This
deformation of the planet's surface is shown in gray along the outer
surface of the planet in this image. The amount of deformation is
highly exaggerated to make it visible here. The actual uplift in
Tharsis is estimated to be about 8 kilometers (5 miles) at its center.
This uplift also stretches the crust, forming features such as grabens
and Valles Marineris. In addition, the hot,
rising material may melt as it approaches the surface, producing volcanic activity. [Simulation & caption by Walter
S. Kiefer and Amanda Kubala, LPI.]
Valles Marineris
This great rift canyon on Mars has a length of 2400 miles (it would
reach from Washington, DC to Los Angeles), a maximum width of 70
miles, and a maximum depth of 22,000 feet. It is vastly
larger than
the US "Grand" Canyon, which would barely qualify as a "side channel"
here. Valles Marineris was not produced by water flow (although many
smaller Martian channels were). Instead, it appears to have formed by
a stretching and tearing of the Martian crust during the Tharsis plume upwelling event. [From Viking
images.]
Ganges Chasma
A collapsed section of the south wall of Valles Marineris. The
transected crater is 10 miles across. The cliff walls are about
20,000 feet high, and the canyon is about 100 km wide. Click on the
image for a wide field view of another set of mega-landslides in the
northern Ophir Chasma canyon of Valles Marineris. [From
Viking images.]
MGS Closeup of Valles Marineris Rim
Closeup of the rim of Valles Marineris showing details of cliff walls,
thousands of feet high. Layering is visible under the rim at the left
hand side. On Earth, such layers can be produced by both sedimentary
and volcanic processes. Both are also possible on Mars. Original
Mars Global Surveyor image has a resolution of 20 feet per pixel.
[Image by Malin Space Science Systems.]
Hellas Impact Basin
MOLA map of the Hellas impact basin, the largest on Mars. The upper
panel shows a cross section through the basin. It is 1400 miles
across and over 29,000 feet deep from the rim to its lowest point
(enough to accommodate Mt.Everest). It is surrounded by a huge volume
of excavated material, which, distributed evenly, would cover the
continental US to a depth of 2 miles. It is in the same league with,
but slightly smaller than, the Aitken basin
on the Moon. Here is a
graphic comparison of the two largest basins on Mars with the US.
Hellas is one of the few major topographic features on Mars that were
readily identified with telescopes on the Earth (see the best
Earth-based map here.)
[Image by MOLA team]
Water on Mars: Sedimentary Layering
This image from MGS shows a part of the floor of the Candor Chasma
canyon, about 0.5 mile wide. It contains a number of layers of
material, each about 30 feet thick. Here and here are similar layered regions. On Earth, deposits
like this form from sedimentary deposits at the bottom of a lake.
This is strong circumstantial evidence for water on Mars at an earlier
time. If these are sediments, they might contain fossils of ancient
Martian lifeforms. Similar features might be produced by lava flows
or windblown dust deposits, but their ubiquity on Mars suggests water
is involved. [Image by Malin Space Science Systems]
Water on Mars: Ravi Vallis
A Viking mosaic of the Ravi Vallis channel. Unlike
Valles Marineris, this channel was carved by water. The region shown
is about 225 mi long.
Like many other channels that empty into the northern plains of Mars,
Ravi Vallis originates in a region of collapsed and disrupted
("chaotic") terrain within the planet's older, cratered highlands.
Structures in these channels indicate that they were carved by liquid
water moving at high flow rates (up to 1000's of times the outflow of
the Amazon river). The abrupt beginning of the channel, with no
apparent tributaries, suggests that the water was released under great
pressure from beneath a confining layer of frozen ground. As this
water was released and flowed away, the overlying surface collapsed,
producing the disruption and subsidence shown here. Three such regions
of chaotic collapsed material are seen in this image, connected by a
channel whose floor was scoured by the flowing water. The flow in this
channel was from west to east (left to right). This channel ultimately
links up with a system of channels that flowed northward into Chryse
Basin. [Image & caption: LPI]
Water on Mars: Runoff Channels
These networks of smaller tributaries leading to larger channels resemble
those produced by ground water flow (rather than rain) on Earth. Click
for enlargement.
[Image by Calvin J. Hamilton.]
Water on Mars: Ares Vallis, The Pathfinder Site
A plain showing prominent scars of catastrophic flooding, probably 1-3
Byr ago. This is an artist's rendering, based on a Viking orbiter
mosaic, with identifications for the more prominent features. The
original photograph can be found here. The arrow shows the initial
landing zone targeted for the Mars Pathfinder in July 1997. Note the
"Wahoo" crater(!) [Painting by NASA. Images from NSSDC.]
Water on Mars: Frozen Lake in Crater
This image of a crater in near the Martian North Pole was taken
by the High Resolution Stereo Camera on the Mars Express orbiter.
It shows a large lake of water ice. The temperature when the image
was taken was above the sublimation temperature of carbon dioxide
("dry") ice, so the material must be water ice. The lake is about
10 km (33,000 ft) across.
Water on Mars: Ancient Ocean Beds?
This is a MOLA elevation map of the north polar hemisphere, with the
outline of the US added for scale. It shows a huge depression which
has many characteristics expected for an ancient ocean bed. Its
border is level in elevation, like a coastline; terraces run parallel
to the coastline; its floor is smooth and relatively flat, suggesting
sedimentation; it is "fed" by channels running from south to north.
Its volume is consistent with other estimates of the total volume of
water on Mars. [Image by MOLA Team]
Water on Mars: Ice Under the South Pole
This picture shows a map made with the MARSIS ground-penetrating radar
instrument on the Mars Express orbiter (March 2007). The radar is
reflected from regions up to 13,000 feet below the surface of Mars'
South Pole, and the image shows the thickness of the layers of water
ice. This is the largest water reservoir yet detected on Mars. If
distributed uniformly over the Martian surface, it would cover the
planet 36 feet deep in liquid water. But the flood plains seen
on the surface suggest that there was over 10 times as much water
originally present on Mars. [Image from Mars Express]
Water on Mars: Volume
Spectroscopic
measurements of molecular hydrogen with the FUSE satellite provide
an estimate of the total volume of water once present on Mars:
the equivalent of a global Martian ocean some 4000 feet deep.
The image above is an artist's concept of what Mars might have looked
like when all its low-lying areas were filled with water.
Last modified
April 2008 by rwo
Text copyright © 1998-2008 Robert W. O'Connell. All
rights reserved. These notes are intended for the private,
noncommercial use of students enrolled in Astronomy 121 at the
University of Virginia.
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