This image of Mars was taken by the Hubble Space Telescope, on February 25, 1995. It is the northern spring, and most of the carbon dioxide 'dry ice' around the pole has gone, leaving only the water ice. Visible features include the extinct volcano Ascraeus Mons, 25 km high and 402 km across, (above the cloud deck on the left) and the Valles Marineris (lower left).
Source: Philip James (University of Toledo), Steven Lee (University of Colorado), NASA.
Average Distance from the Sun: 227.94 million km (1.54 AU)
Size (Equatorial Diameter): 6 787 km (0.532 x that of Earth)
Mass: 6.57 x 1023 kg (0.11 x that of Earth)
Length of Day (Solar Rotation Period): 24.62 Earth hours
Length of Year (Sidereal Orbital Period): 686.98 Earth days
Temperature: -20° C (summer) -140° C (winter)
Gravity: 3.72 m/s2 (0.38 x that of Earth)
Mars is the last of the four terrestrial or rocky planets of the inner Solar System. Visible in our night skies as a bright, reddish object, it has been known since ancient times. Historically, Mars has occupied a popular place in the human imagination as a potential home for alien life. It has inspired many Science Fiction stories, most notably The War of the Worlds by H. G. Wells, but also speculation by people such as Percival Lowell, an amateur astronomer at the end of the last century who believed there were 'canals' on the surface of Mars.
The terrain around the Mars Pathfinder landing site, with the Sojourner rover in the foreground.
Source: Courtesy NASA/JPL-Caltech
The Viking space probes which visited Mars in 1975 found it to be devoid of life. Then, in 1996, NASA announced that a meteorite, found in Antarctica in 1984, came from Mars and possibly contained evidence of fossilised bacteria from 3.5 billion years ago. Scientists today still disagree on these results and what they mean. Visit NASA's Astrobiology News & Events webpage for the lastest in the 'Life on Mars?' debate.
On July 4th, 1997, the Mars Pathfinder probe landed on Mars and released its surface rover Sojourner, which studied the Martian landscape. Over the next few years other probes, such as Mars Global Surveyor, will visit Mars and in 2005 a probe will return a sample of Martian rock to Earth.
The surface of Mars is made of rock, covered with thick powdery red soil. Rocks and boulders of all sizes litter the soil. There are many long, narrow, twisting valleys which may once have been rivers but are now completely dry.
A huge canyon called the Valles Marineris stretches across the Martian surface. In places it is 7 km deep and is 4 000 km long, about the distance from Perth to Sydney. The surface is also pitted with craters. There are some huge volcanoes on Mars which appear to be extinct, but may only be dormant. The largest of these is the giant Olympus Mons, which is 27 km high, three times the height of Mt Everest. It is the largest volcano in the Solar System.
In winter, the poles are covered with a thick layer of 'dry ice', or frozen carbon dioxide. This disappears during the Martian summer. Below this is a smaller, permanent core of water-ice, a few hundred kilometres across.
The atmosphere on Mars is very thin. It consists mainly of carbon dioxide and there is very little oxygen.
Sometimes huge areas of the planet experience violent dust storms. Winds reach speeds of up to 200 km per hour and dust billows up as high as 10 km into the atmosphere, turning the sky a deep pink. These storms may last for weeks.
Mars has two small, irregular moons:
Phobos (diameter: 20x23x28 km)
Deimos (diameter: 10x12x16 km)
Both have heavily cratered surfaces and may have been asteroids captured by the planet.
Mars was the Roman god of war and agriculture. He had a highly developed cult at Rome and was particularly revered by the army. He gave his name to the month of March. His agricultural role was honoured with festivals in May. Romans believed him to be the son of June, impregnated by a flower. To the ancient Greeks he was Ares, son of Zeus.