World

Phobos

Phobos is the larger of Mars’s two moons, a lumpy rock spiralling in towards Mars by 1.8 m a century, about 22 km across.

Key facts

Diameter

22 km

Goes round

Mars

See it from here

Not by eye: Phobos is magnitude 11.3 at its best and hugs Mars, whose glare drowns it; it was found in 1877 with a 26-inch telescope.

How the map draws it

Drawn in its measured shape · its surface is a black-and-white mosaic, tinted in a colour chosen from published descriptions · lit as a camera exposed for its own sunlight would show it · seen from far off it is a light at its computed brightness: the glow is how a camera records a point too bright to resolve.