♂︎Mars

STATISTICS

ORBITAL RADIUS

230 million km from the Sun (1.5 times the distance of the Earth from the Sun)

ORBITAL PERIOD

687 Earth days (1.9 Earth years)

DIAMETER

6,800 km (0.5 times the diameter of the Earth)

ROTATIONAL PERIOD

24.6 Earth hours

MASS

11% of the mass of the Earth

SURFACE GRAVITY

about two-fifths of the gravitational force on Earth

ALBEDO

0.15

MOONS

Mars has two very small moons.

Phobos (which has an average diameter of 22 km) and Deimos (which has an average diameter of 12km).

Phobos orbits at a distance of around 9,000 km from the centre of Mars (6,000 km above the surface), taking about seven and a half (Earth) hours to complete an orbit.

Deimos orbits at a distance of around 23,000 km from the centre of Mars (20,000 km above the surface), taking about thirty (Earth) hours to complete an orbit.

Phobos is doomed — it is (very) slowly spiralling towards the surface of Mars. In around 100 million years, when it gets close enough to Mars (when it reaches the Roche limit) it will be ripped apart by tidal forces and will form a (very thin) ring around Mars. Deimos, on the other hand, is slowly spiralling away from Mars (in the same way that our own Moon is slowly spiralling away from the Earth).

Phobos is Greek for ‘fear’ (as in phobia) and Deimos means ‘dread’; they were the sons of Ares, the Greek god of war. (Mars is the Roman god of war, so the names are a bit muddled.)