Mars: A Century of Exploration
The Moons: Phobos and Deimos
Mars has two moons, Phobos and Deimos, which were discovered in 1877. Both
are thought to be C-type asteroids (which resemble the class of
"carbonaceous chondrite" asteroids) which were "captured" by Mars.
Phobos
is in an orbit 9,380 km from Mars and has a period of less than 8 hours
(making the Martian month shorter than the Martian day!).
It is about 26
km long.
Deimos is in an orbit 23,460 km from Mars and has a period of
about 30 hours. It is about 10 km long.
Our first close-up look of these moons came with the Mariner 9 probe.
This is a Viking 2 orbiter image of Deimos from a distance of 500 km.
The surface appears smooth,
but many craters are partially hidden by regolith (that is, by the
soil and broken-up material).
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