Mars

The Bringer of War

Mars Facts

• Mars is the fourth planet from the Sun and the seventh largest:
  • distance from Sun: 227,940,000 km (1.52 AU)
  • diameter: 6,794 km
  • mass: 6.4219e23 kg

• Mars (Greek: Ares) is the god of War. The planet probably got this name due to its red color. Mars is sometimes referred to as the Red Planet. (An interesting side note: the Roman god Mars was a god of agriculture before becoming associated with the Greek Ares; those in favor of colonizing and terraforming Mars may prefer this symbolism.) The name of the month March derives from Mars.

• Mars has been known since prehistoric times. It is still a favorite of science fiction writers as the most favorable place in the Solar System (other than Earth!) for human habitation. But the famous "canals" reported by Lowell and others were, unfortunately, just as imaginary as Barsoomian princesses.

• The first spacecraft to visit Mars was Mariner 4 in 1965. Several others followed including the two Viking landers in 1976.

• Mars's orbit is significantly elliptical. One result of this is a temperature variation of about 30 C at the subsolar point. Overall, the Viking landers found that Martian temperatures vary from 150 K (-220 F) to 295 K (70 F).

• Though Mars is much smaller than Earth, its surface area is about the same as the land surface area of Earth.

• Except for Earth, Mars has the most highly varied and interesting terrain of any of the terrestrial planets, some of it quite spectacular:
  • Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km (20,000 ft) high (picture 8).
  • Tharsis: a huge bulge on the Martian surface that is about 4000 km across and 10 km high.
  • Valles Marineris: a system of canyons 4000 km long and from 2 to 7 km deep (picture 1, above).
  • Hellas Planitia: an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter (picture 4).
  Much of the surface is very old and cratered (picture 14), but there are also much younger rift valleys, ridges, hills and plains.

• The southern hemisphere of Mars is predominately ancient cratered highlands. Most of the northern hemisphere is much younger and is also much lower in elevation. An elevation change of several kilometers occurs at the boundary. The reason for this division is unknown.

• The interior of Mars is known only by inference from data about the surface and the bulk statistics of the planet. The most likely scenario is a dense core about 1700 km in radius, a molten rocky mantle somewhat denser than the Earth's and a thin crust. The lack of a global magnetic field indicates that Mars's core is probably solid. Mars's relatively low density compared to the other terrestrial planets indicates that its core probably contains a relatively large fraction of oxidized material.

• Like Mercury and the Moon, Mars appears to lack active plate tectonics; there is no evidence of horizontal motion of the surface such as the folded mountains so common on Earth. With no lateral plate motion, hot-spots under the crust stay in a fixed position relative to the surface. This, along with the lower surface gravity, may account for the Tharis bulge and its enormous volcanoes.

• There is very clear evidence of erosion in many places on Mars. At some time in the past there was clearly water on the surface (picture 11). There may even have been oceans. But it seems that this occurred only briefly and very long ago; the age of the erosion channels is estimated at about 4 billion years. (Valles Marineris was NOT created by running water. It was formed by the stretching and cracking of the crust associated with the creation of Tharsis.)

• Early in its history, Mars was much more like Earth. As with Earth almost all of its carbon dioxide was used up to form carbonate rocks. But lacking the Earth's plate tectonics, Mars is unable to recycle any of this carbon dioxide back into its atmosphere and so cannot sustain a significant greenhouse effect. The surface of Mars is therefore much colder than the Earth would be at that distance from the Sun.

• Mars has a very thin atmosphere composed mostly of the tiny amount of remaining carbon dioxide (95.3%) plus nitrogen (2.7%), argon (1.6%) and traces of oxygen (0.15%) and water (0.03%). The average pressure on the surface of Mars is only about 7 millibars (less than 1% of Earth's), but it varies greatly with altitude from almost 9 millibars in the deepest basins to about 1 millibar at the top of Olympus Mons. But it is thick enough to support severe winds and vast dust storms that on occasion engulf the entire planet for months. Though like Venus, the atmosphere is mostly carbon dioxide, Mars's greenhouse effect is only enough to raise the surface temperature by 5 degrees (K).

• Mars has permanent ice caps at both poles (picture 7) composed mostly of solid carbon dioxide ("dry ice"). In the northern summer the carbon dioxide completely sublimes, leaving a residual layer of water ice. It's not known if a similar layer of water ice exists below the southern cap since its carbon dioxide layer never completely disappears. There may also be water ice hidden below the surface at lower latitudes. The seasonal changes in the extent of the polar caps changes the global atmospheric pressure by about 25% (as measured at the Viking lander sites).

• Recent observations with the Hubble Space Telescope (picture 3) have revealed that the conditions during the Viking missions may not have been typical. Mars's atmosphere now seems to be both colder and dryer than measured by the Viking landers. (more details from STScI)

• The Viking landers (picture 17) performed experiments to determine the existence of life on Mars. The results were negative. Optimists point out that only two tiny samples were measured and not from the most favorable locations. More experiments will be done by future missions to Mars.

• A small number of meteorites (the SNC meteorites) are believed to have originated on Mars.

• Mars has no global magnetic field.

• When it is in the nighttime sky, Mars is easily visible with the naked eye. Its apparent brightness varies greatly according to its relative position to the Earth. Mike Harvey's planet finder charts show the current position of Mars (and the other planets) in the sky.

Pictures

1. (above) Valles Marineris from USGS mosaics 83k gif; 241k jpg
2. Valles Marineris 678k gif 116k jpg

3. Mars by HST WFPC2 Feb 95 34k jpg; 158k gif

4. Hellas region from USGS mosaics 61k gif; 131k jpg

5. Schiaperreli region from USGS mosaics 94k gif; 359k jpg; 263k gif; 70k jpg;

6. Syrtis region from USGS mosaics 74k gif; 256k jpg

7. South Pole 153k gif; 99k jpg

8. Olympus Mons 128k jpg

9. Olympus Mons perspective 36k jpg; 211k gif
10. Mars (three color -red,green,blue- composite) by HST Planetary Camera 52k jpg
11. Possible erosion channel on Mars, false color 199k gif
12. Viking image of Mars showing a valley and what appears to be a delta 697k gif

13. South Candor Chasma 147k gif; 145k jpg

14. Sinus Sabaeus and Deucalionis Regio gif

15. Viking lander on martian ground (B&W) 69k gif
16. View from Viking 1 Lander 190k gif; 99k jpg

17. Viking 2 Lander Site 137k gif; 610k jpg

18. "The Face" (an oddly shaped hill or a monument to Elvis?) 9k jpg; 10k gif

19. Viking lander images html

20. Digital Image Model 166k jpg

21. ... more Mars images

Movies

1. Mars globe rotating (CCD images) 47k fli
2. Mars Rotating Globe Animation 721 frames (very nice!) 725k mpg
3. Video clip from Mars the Movie 12000k AVI
4. Flight over Valles Marineris 1500k AVI
5. Small animation shows the Mars' globe (CCD images) 105k FLI
6. Hubble Telescope full-globe animation 757k MPEG

Mars's Satellites

           Distance  Radius    Mass
Satellite  (000 km)   (km)     (kg)   Discoverer  Date
---------  --------  ------  -------  ----------  ----
Phobos            9      11  1.08e16  Hall        1877
Deimos           23       6  1.80e15  Hall        1877

More about Mars, Deimos, and Phobos

• from ASU
• from LANL
• from JPL
• from RPIF
• from RGO
• from NASA Spacelink
• Volcanoes on Mars by James R. Zimbelman of NASA
• Martian Volcanoes from LANL
• Martian Clouds from LANL
• The Martian Chronicle, The Electronic Newsletter for Mars Exploration at JPL
• from NSSDC
• Center for Mars Exploration
• Mars Atlas and Viking Orbiter image-finder (access high-res images of the entire surface of Mars!)
• Mars Page from Malin Space Science Systems
• more about "The Face" from MSSS (another copy of it at LANL); a teacher's guide about "The Face" by Sally Stephens of PASP
• images of the "Happy Face" from MSSS
• Marslink Essays by Mike Caplinger
• Mars Today: html; ~100k gif
• Meteorology Data from the Viking landers (and some images)
• The Daily Martian Weather Report from Mars Global Surveyor Radio Science Team at Stanford
• Images of Mars (ExInEd Hypercard stack)
• Dr. Cain's class notes
• Mars Nomenclature Table

Open Issues

• Why are the northern and southern hemispheres of Mars so different? Why are the northern and southern polar caps different?
• Is there still active volcanism on Mars?
• What exactly caused the erosion patterns that look so much like stream beds on Earth?
• How much subterranean (submartian?) water is there?
• Mars remains at the top of the list of possible life-bearing planets. The Viking probes found no evidence of life on Mars. But they sampled only two isolated locations. Is there life elsewhere or was there life at some time in the past on Mars? The probability seems rather low, but the impact of a positive result would be enormous.
• The future of Mars exploration is uncertain. The two most recent Soviet probes failed. The Russian missions Mars 94 and Mars 96 have been delayed until at least 1996 and 1998. NASA's Mars Observer was lost just before it reached Mars. Mars Surveyor (which includes most of the science instruments from Mars Observer) program barely survived its passage through Congress this year. NASA's Mars Pathfinder seems to be on track but future missions in both the USA and Russia are in financial danger.

Express to Jupiter