Credit: NASA

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The fourth planet from the Sun, long called the 'Red Planet' for its reddish appearance caused by ferric atmospheric and surface dust.

• ORBIT: 227.9 million kilometres is the mean distance from the Sun, about 1.5 times the distance between the Sun and Earth.

• DIAMETER: 6,794 km, slightly more than half the Earth's diameter.

• RADIUS: 3,397 km, around half the Earth's radius.

• MASS: 6.4185 x 10 ²³ kg, 0.107 x Earth's mass.

• GRAVITY: 0.38 x Earth's gravity.

• MARTIAN DAY: 24 hours, 37 minutes, 22 seconds.

• MARTIAN YEAR: 669 Martian days (687 Earth days).

• TEMPERATURE: Average –55 ºC. Minimum: -133 ºC at the poles in winter. Maximum temperature: 27 ºC in summer on equator.

• ATMOSPHERE: Composition 95.3 per cent carbon dioxide (CO₂), 2.7 per cent nitrogen, 1.6 per cent argon, 0.1 per cent oxygen.

• ATMOSPHERIC PRESSURE: Pressure at surface is less than 1/100th Earth's atmospheric pressure.

• LANDSCAPE: Rocky, dusty and dry. The northern hemisphere is smooth and flat, while the southern hemisphere comprises deeply cratered, rugged highlands. Oceans once covered Mars' surface, and residual water in the form of ice lies at the polar caps and, possibly, in abundance close to the surface in other regions. The north pole has a large, permanent cap of what is believed to be mainly water ice. The south pole has a small cap, possibly of frozen CO₂, which almost disappears during the Martian summer.

• MAJOR FEATURES: Olympus Mons, at 26 km, the highest known volcano in the solar system; Tharsis Dome, a mysterious bulge 10 km high and 4,000 km across; Valles Marineris, a canyon 4,000 km long and up to seven kms (4.4 miles) deep.

• MOONS: Phobos, diameter 22 km, orbit 5,981 km from surface; Deimos, diameter 12 km, orbit 20,062 km from surface.