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 of orbiters and landers which began in the mid-1990's has yielded 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.

Earth, Moon, Mars

Earth, Moon, and Mars Compared to Scale


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), here (details), or in a large-format poster here.

The Tharsis hemisphere is dominated by the "Tharsis Bulge" a huge, elevated 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.

[Images: MOLA Team]


Map of Tharsis

MOLA map of the dramatic Tharsis (left) and Chryse (right) regions on Mars, color-coded for altitude as above. Click on the map for a high-resolution image of the area.

Clearly marked are the major Tharsis volcanoes: Olympus Mons (the isolated peak to the west at coordinates 18N, 228E), Alba Patera (40N, 250E) and the volcanic chain consisting of Ascraeus, Pavonis and Arsia montes. 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, running toward the northern plains. The large red (high altitude) blotch corresponds to the "Tharsis Bulge."

Although the Tharsis Bulge itself is thought to be over 3 billion years old, volcanic activity in the form of smooth lava flows continued in some areas there until as recently as 100 million years ago. There is even improving evidence that some small flows occurred in the last few million years. Mars may not be quite as dormant a planet as had been assumed.

[Image: 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.
OM Caldera

Caldera of Olympus Mons (Viking)

Apollinaris Patera

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

Ceraunius Tholus

A Viking vertical view of Ceraunius Tholus, a "small" volcano in the Tharsis Bulge just north of the chain of three large Tharsis volcanos described above. Ceraunius is about 21000 feet high; the caldera 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. Here is a perspective view, created in software from Mars Express images, from the top of Ceraunius' caldera. Gigantic stress fractures caused by the upwelling of magma from below cross this region. Click the image for an enlarged view.

Mantle Plume

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

Valles Marineris

This great rift canyon on Mars, seen here in a Viking mosaic image, 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. Here is a video animation (9 MB) of a "flyover," based on Mars Odyssey images, which gives a good sense of the scale and structure of Valles Marineris.

Ganges Chasma

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.]

Valles Marineris Rim, MGS

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 Basin

Hellas Impact Basin

A 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]

Views of Mars' Northern Polar Cap

The frame at the left shows Mars' northern polar cap shrinking from its maximum size in winter to its minimum in summer (images taken from near-Earth orbit by the Hubble Space Telescope). In winter the cap is predominantly frozen carbon-dioxide ("dry ice"), whereas the persistent summer cap consists of water ice. The spiral patterns that emerge in summer are enlarged in the MGS image at the right, which has been digitally rendered by R. Kosinski. The patterns are shaped by strong windflows. The long, dark indentation is Chasma Boreale, a 300-km long canyon reaching almost through the polar cap.

Chasma Boreale

The Cliffs of Chasma Boreale

A perspective view, constructed from High Resolution Stereo Camera images (Mars Express orbiter), showing parts of the canyon walls of Chasma Boreale in summer. The cliffs here are nearly 2-km (6500 ft) high. The layered terrain is evident in the image. Residual frost is water ice.



A Mars Express view of the strange Cydonia region, on the Martian northern Acidalia Planitia lowlands. The many sharply defined elevated regions have evidently been heavily eroded by water flows. Cydonia elicted great excitement when the Viking spacecraft first returned a low-quality image that appeared to show a gigantic, carved human face in the region (in the lower right corner of this image). Later, high resolution imaging showed that the "face" was a completely natural formation, although some enthusiasts continue to argue that Cydonia contains artificial structures. See Guide 23 for more discussion of the "face." Click for a full-resolution version of the image.


Kasei Valles Boundary

A high-resolution view from the Mars Express orbiter of the boundary between the large outflow canyon system Kasei Valles (upper area) and the Lunae Planum plateau (lower left). Kasei Valles runs northward from near Valles Marineris and feeds into the the northern lowlands/ocean basin. North is to the right in the image. The jumbled terrain was scoured by gigantic water flows in the past, which also eroded the upper wall of the 22-mile diameter crater at the right of the image. The volume of water involved was several thousand times the flow of the Amazon River. Click for a much enlarged image.

Kasei-Valles with altitude coding

Kasei Valles Boundary With Altitude Coding

The same region shown above but with pseudocolor coding for altitude. The coding is shown in the upper right. Click for a much enlarged image.

Acidalia Channels

Acidalia Planitia Channels

A high-resolution view from the Mars Express orbiter of a region about 600 miles northeast of the previous image. This shows the channels feeding into the northern Acidalia Planitia lowlands (below) from the Tempe Terra plateau (above). Color-coded for altitude; blue indicates the lowest altitude. Resolution is 15-m per pixel. Note the older craters that have been filled in/submerged by wind or water-borne material.


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. Click for a full-scale version. [Image by Malin Space Science Systems]

Ravi Vallis

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 (as opposed to rain) on Earth. Click for enlargement. [Image by Calvin J. Hamilton.]

Ares Vallis

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 added for the more prominent features. 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: Hematite "Blueberries"

The Mars Exploration Rover "Opportunity" took this close up of the surface near its landing site showing thousands of tiny spherules called "blueberries" because of their blueish tint in false-color images. They contain hematite, an iron-oxide mineral precipitated from water. Such "concretions" are also found on Earth.

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: Distribution of Water Molecules

This is a map of the fractional content of water molecules in the upper 1-meter or so of the Martian surface. It was obtained by the Gamma Ray Spectrometer experiment on the orbiting Mars Odyssey spacecraft. This instrument detects gamma rays emitted by hydrogen atoms on the surface after they are activated by penetrating cosmic rays. Some regions of the surface are quite dry, but most contain significant water, and both poles are rich in water molecules. The gamma-ray technique allows other individual elements to be mapped as well, including silicon, chlorine, and iron. [Image from Mars Odyssey]

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. The black circle is an area without data. 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 in the Martian atmosphere 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.

Curiosity on Mars

At the left is a self-portrait of "Curiosity," the rover of NASA's Mars Science Lander mission, at it looked on the surface of Mars in February 2013. It carries the most sophisticated set of geophysical analysis instruments ever sent to another planet. In a complex landing sequence Curiosity was placed within 1.5 miles of its intended landing site in Gale Crater on August 6, 2012. This 96-mile diameter crater contains a large central mountain (Aeolis Mons or "Mt. Sharp") composed of sedimentary rock. At right is a telephoto view of Aeolis Mons taken by Curiosity, showing its layered structure. Curiosity is exploring the flanks of the mountain. Click on the images for enlargements. To follow Curiosity's progress, check the Curiosity Rover mission site at JPL.

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Last modified December 2020 by rwo

Original text copyright © 1998-2020 Robert W. O'Connell. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 1210 at the University of Virginia.