Mars is the fourth planet from the sun and the seventh largest
SurfaceMars is smaller than the earth but has the same surface area, and has the most highly varied and interesting terrain of any planet in the Solar System other than earth. It has the largest mountain in the solar system, a very large system of canyons and an impact crater. Much of Mars surface is old and cratered but it also has younger rift valleys ridges, hills and plains. The southern hemisphere is mainly cratered highlands and the northern hemisphere has younger lower plains with an abrupt elevation change of several kilometers at the boundary. Mars' red surface colour is due to iron on the surface soil long ago reacting with the tiny amount of oxygen still on Mars, making rust.
InteriorMars' interior is most likely to consist of a dense core, a molten rocky mantle and a thin crust. The crust is approximately 80km thick in the southern hemisphere and 35km thick in the northern hemisphere. Mars is not a dense planet partly due to the crust being composed of sulfur as well as iron. The planet lacks active plate tectonics, so hot-spots under the crust stay in fixed positions. This and low gravity account for the large number of volcanoes, although there is no evidence that these are currently active.
AtmosphereThe very thin atmosphere is composed of small amounts of carbon dioxide and nitrogen with traces of argon, oxygen and water. Almost all the carbon dioxide on the planet was used to form carbonate rocks and because there are no plate tectonics, no carbon dioxide is currently recycled back into the atmosphere. This therefore means that a greenhouse effect can only sustain a temperature rise of 5 degrees making Mars' surface very cold. The thin atmosphere cannot block harmful solar radiation. Although the atmosphere is thin it can still support strong winds and vast dust storms that can engulf the planets for months. The average pressure is 7 milibars but it varies with altitude.
TemperatureThe temperature varies due to Mars elliptical orbital, but the average temperature is 218K.
MagnetismLarge, but not global, weak magnetic fields exist in various regions, probably remnants of an earlier global field since disappeared.
PolesPermanent ice caps occur at both poles mainly composed of solid carbon dioxide (dry ice). The ice caps have a layered structure of alternating layers of ice with varying concentrations of dark dust. The mechanism for the layering maybe due to climate changes related to long term changes in the inclination of Mars' equator to the plane of its orbit. In the northern summer, the carbon dioxide sublimes leaving a residual layer of water ice. The seasonal changes in the extent of the polar caps changes the global atmospheric pressure by about 25%.
LifeIn 1996, David McKay et al announced the first identification of organic compounds in a Martian meteorite. The authors further suggested that these compounds maybe evidence of ancient Martian microorganisms living on the planet 3.6 billion years ago when Mars was warmer and wetter. The evidence is strong but by no means establishes the fact of extra terrestrial life, and there are several contradictory studies.
WaterA new discovery shows that there maybe current sources of liquid water at or near the surface of Mars. Gullies formed by flowing water and deposited of soil and rocks transported by flows were found and appeared so young that they maybe forming at the present day.
Mars
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