The Universe and Galaxies: Mars

Discovery Space: Mars

Mars is only half as large as the Earth, and it is enclosed by a thin atmosphere. From all the planets of the solar system, its surface conditions are closest to those on Earth-so it has long been of great interest to science.

Mars is 1.5 times further from the sun than the Earth. It is known as the Red Planet due to its rusty coloration, as its sur- face is high in iron oxide. The rotation of Mars on its axis takes 24.6 hours. It is orbited by two moons: Phobos, with a diameter of 16 miles (27 km), and Deimos, diameter nine miles (15 km).


Mars’s atmosphere consists of 95 percent carbon dioxide, 3 percent nitrogen, and small amounts of argon, oxygen, carbon monoxide, and water vapor. The atmosphere is thin with a ground pressure varying between four and nine milli- bars. By comparison, the atmospheric pressure on Earth at sea level is 1,013 millibars; therefore without a pressurized suit and an oxy- gen supply a human could not survive.

Only a little heat can be stored by the thin atmosphere, and temperature differences are extreme. They can vary between -112°F(-80°C)and68°F (20°C) at the Equator.

The surface

Mars’s atmosphere must once have been denser, as river valleys with streamlined islands indicate the presence of running water. Nowa-
days, water can only last in the form of ice or water vapor, although the presence of liquid water underneath Mars’s surface is still possible.

By means of radar measurements made by the European space probe, Mars Express, water ice has now been dis-covered at the south pole, embedded deep within the ground. The surface of Mars resembles a rocky desert. The northern plains, flattened by lava flows, contrast with the southern highlands, which have huge impact craters.

The volcano Olympus Mons is the highest mountain in the solar system, reaching 16 miles (26 km) above the lowland-three times higher than Mount Everest. The Valles Marineris is part of an enormous trench system across the planet. It extends for more than 2,485 miles (4,000 km) and in places is four miles (seven km) deep.


Biochemical data taken by the Viking probes during the 1970s may indicate the presence of microorganisms on Mars. Another indication of life in the Mars atmosphere is the presence of methane.

This could have developed geochemically or from the metabolism of microorganisms. Meteorites from Mars have also shown possible evidence of fossilized microorganisms.


DIAMETER of Mars: 4.221 miles (6,794 km)

DISTANCE of Mars to the sun: 142 million miles (228 million km)

ORBIT of Mars around the sun: 687 days