ORBIT: 227.9 million kilometers (142.4 million miles) mean distance from the Sun, about half as much again as the distance between the Sun and Earth.

DIAMETER: 6,794 kms (4,246 miles). By comparison, Earth's diameter is 12,756 kms (7,973 miles)

MARTIAN DAY: 24 hours 37 minutes and 22 seconds

MARTIAN YEAR: 669 martian days (687 Earth days)

TEMPERATURE: Average - 55 C (- 67 F). Minimum: - 133 C (- 207.4 F), at the poles in winter. Maximum temperature: 27 C (80.6 F) in summer on equator

ATMOSPHERE: Composition 95.32 percent carbon dioxide (CO2), 2.7 percent nitrogen, 1.6 percent argon, 0.13 percent oxygen. Pressure at surface is less than 1/100th Earth's atmospheric pressure.

LANDSCAPE: Rocky, dusty and dry, although some scientists speculate water lurks close to surface. Northern hemisphere is smooth and flat, southern hemisphere is deeply cratered, rugged highlands. North pole has a large, permanent cap of what is believed to be mainly water ice. South pole has a small cap, which may be frozen carbon dioxide (CO2) and almost disappears during the martian summer.

MAJORS: Olympus Mons, at 26,000 metres (84,500 feet), the highest known volcano in the Solar System; Tharsis Dome, a mysterious bulge 10 kms (six miles) high and 4,000 kms (2,500 miles) across; Valles Marineris, a canyon 4,000 kms (2,500 miles) long and up to seven kms (four miles) deep.

MOONS: Phobos, diameter 22 kms (13.75 miles), orbit 5,981 km (3,738 miles) from surface; Deimos, diameter 12 kms (eight miles), orbit 20,062 kmsmiles) from surface.

SPACE.WIRE