Phobos

Moon

The larger of Mars's two moons, orbiting so close and fast it rises twice a day.

Facts

TypeMoon
OrbitsMars
Distance from parent body9,376 km
Diameter22 km
Mass1.07 × 10^16 kg
Surface gravity5.70e-3 m/s²
Temperature-40°C
Orbital period0 days
Apparent magnitude11.8
Redshift0
Discovered1877

Phobos in context

At 22 km across, Phobos is 0.6 percent of the diameter of Earth's Moon.

Its mass is less than a thousandth of the mass of Earth.

It orbits Mars at 9,376 km, closer in than the Moon orbits Earth.

A single orbit takes 7.7 hours.

An average temperature of 233 K works out at -40 degrees Celsius, colder than the 15 degrees Earth averages.

It has been on record since 1877.

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