Mars

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

Vital Statistics

Fourth planet from the Sun
Rather eccentric orbit. Average distance from the Sun is 142 million miles
- Perihelion distance 128.6 million miles,
- aphelion distance 160 million miles.
Takes 687 days to orbit the Sun.
Distance from Earth varies from 36 million miles (nearest planet after Venus) to over 250 million miles. Proportionately, this six-fold distance variation is the greatest of any planet.
Diameter 4225 miles.
Rotates in 24-1/2 hours.

Mars has an atmosphere which is about 95% carbon dioxide, with small amounts of nitrogen argon, and oxygen.
The atmospheric pressure ranges from one-half percent to one percent that of Earth.
Surface temperatures are in the range -30F to -200F.
Mars has clouds of mostly water ice but some frozen carbon dioxide.
Dust storms occur on Mars and sometimes obscure the planet as seen from Earth.
Mars has two polar ice caps which are thin layers of water ice and carbon dioxide frost.
The polar caps expand and shrink with the Martian seasons.

Noachian: 4.6 to about 3.5 to 3.8 billion years ago) Named after Noachis Terra. Heavy cratering but also much evidence of liquid water.

Hesperian: 3.5 to 1.8 billion years ago. Named after Hesperia Planum. Main epoch of volcanic activity, which buried many earlier craters.

Amazonian: From the end of the Hesperian to the present. Named after Amazonis Planitia. Too cold for liquid water at the surface.

Below: a map of Martian albedo features compiled from several observers between 1939 and 1941

Large areas of heavily cratered, probably very ancient crust
Areas where craters have been obliterated by erosion and deposition
An enormous rift valley (Vallis Marineris) which is about 5000 km long, about 100 km wide and nearly 10 km deep.
Extensive signs of water erosion. Channels and flood plains. Rovers have found extensive evidence of water-lain sedimentary rocks.
Enormous volcanoes. Nix Olympica or Olympus Mons is 500 km in diameter and over 20 km high. It is a type of volcano known as a Shield Volcano and is probably made of basalt. The largest shield volcano on Earth, the island of Hawaii, is only about 300 km in diameter and about 10 km high.
Areas of chaotic terrain, possibly large areas of permafrost melting and ground collapse.
Mars is far less active than Earth geologically. Judging from cratering, the active erosion occurred several hundred million years ago.
There is no known surface water on Mars at present.
Areas of laminated (bedded) terrain near the poles of Mars may be wind-deposited sedimentary rocks.
Somewhat denser toward center but not known whether it has a core.
May have a very weak magnetic field.

Early observers thought they could see "canals" on Mars, and some took these to be signs of intelligent life. Now known that canals are myths.
Doubtful whether life could evolve on Mars under present conditions but some simple terrestrial organisms could survive there.
If life had appeared on Mars in the past, it could have adapted to more severe conditions.
No certain signs of life have been noted from space images or from the Viking landers, but the Viking landing sites were chosen for safety and are not the likeliest places to search for life.
In 1997, a Martian meteorite found in Antarctica was announced to show possible evidence of ancient Martian life:
- Distinctive organic molecules
- Minerals typical of those formed by terrestrial organisms
- Possible fossil remains of rod-like organisms
- No single piece of evidence is conclusive. Supporters of Martian life believe the best interpretation of all the evidence together is life
- Skeptics believe the possible fossils are too tiny to contain the molecules necessary for life
- Everyone involved agrees the evidence shows only possible evidence of ancient Martian life.

Mars has two small moons. Both are rather irregular.
Phobos measures about 12 by 18 miles
- Circles Mars about 5800 miles from its center or about 3700 miles above its surface.
- It circles Mars in about 7 hours and 40 min., and is unusual in that it circles its home planet faster than the planet rotates.
Deimos measures about 7 by 10 miles
- Circles Mars at a distance of 14,600 miles (12,500 miles above the surface).
- It takes about 30 hours to orbit Mars.
Both satellites would show tiny "disks" from Mars but would appear much smaller than the Sun would appear (and the Sun would be only 3/4 the size seen from Earth).
Both satellites are heavily cratered. Phobos shows curious grooves that may be fractures caused by a large impact.
The satellites could possibly have formed in orbit around Mars but are more likely captured asteroids.
Escape velocity from Phobos is about 25 mph, and from Deimos about 15.
- You could easily throw a baseball free from either.
- An Olympic high jumper could escape from Deimos and could jump about 3 miles high on Phobos.

Robert M. Haberle, 1986. The Climate of Mars. Scientific American, vol. 254, no. 5, pp. 54-65
Raymond E. Arvidson, Alan B. Binder and Kenneth L. Jones, 1978, The Surface of Mars. Scientific American, vol. 238, no. 3, pp. 76-91
Norman H. Horowitz, 1977, The Search For Life on Mars. Scientific American, vol. 237, no. 5, pp. 52-61
Conway B. Leovy, 1977, The Atmosphere of Mars. Scientific American, vol. 237, no. 1, pp. 34-43
Joseph Veverka, 1977, Phobos and Deimos. Scientific American, vol. 236, no. 2, pp. 30-37
Michael H. Carr, 1976, The Volcanos of Mars. Scientific American, vol. 234, no. 1, pp. 32-43
James B. Pollack, 1975, Mars. Scientific American, vol. 233, no. 3, pp. 106-117

Created 20 May 1997, Last Update 11 January 2020