Solar System information #8: Mars

Mars - the red planet

Mars is the plant most similar to Earth: it is rocky with a tenuous atmosphere. However, this atmosphere is very thin, with less than 1% of the pressure of the Earth's atmosphere. The Martian atmosphere is made up of 95.3% carbon dioxide, 2.7% nitrogen, 1.6% argon, and traces of other gases. The temperature drops rapidly at night because the atmosphere is too thin to retain the daytime heat. There are polar ice caps, made of water-ice and frozen carbon dioxide, which advance and then recede again as the seasons change. A Martian day is slightly longer than an Earth day (24.6 hours).

Mars will probably be the next world visited by mankind; the U.S.A. has plans for manned expeditions to Mars next century. The time spent away from Earth on this expedition would require the astronauts to push their bodies to the limit in the low-gravity environment. The human body declines badly after about 12 months in weightless conditions.

Mars has been investigated with flybys and landings by both the Americans and the Soviets. The first flyby was Mariner 4 from the U.S.A. in 1965. Mariner 9 went into orbit around Mars in 1971 and relayed detailed pictures of the surface. In 1976 the Viking 1 and Viking 2 probes from U.S.A. surveyed Mars in even greater detail with orbiters and landers. The Martian surface has craters, huge dead volcanoes, sandy plains, enormous canyons, extensive areas of erosion (by wind and possibly water), and terraced areas near the poles. Recent research on a Martian meteorite found in Antarctica has given rise to the possibility of bacterial action on Mars at some time during its history, although Martian landers had found no evidence of this in 1976.

Rust-coloured sandy desert covers much of the Martian surface, hence the name "The Red Planet". Dust storms are common, with winds of over 200 km/hr. Sometimes a big dust storm will obscure the face of the planet for months. Major surface features include a giant canyon called Valles Marineris (5,000 km long, up to 400 km wide and 7 km deep) and the massive extinct volcano Olympus Mons which is 25 km high and 600 km across at its base. One of the most puzzling discoveries is the presence of channels similar to stream beds on Earth. This suggests that water once existed in great quantities on the surface of Mars. Where has the water gone? It may be held in a permafrost layer beneath the ground.