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Deimos is the smaller and outermost of Mars’ two moons, named after a character of human mythology.


Deimos is probably an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars, though this hypothesis is still in some dispute. Like most bodies of its size, Deimos is highly nonspherical with dimensions of 15×12×10 km.


Deimos is composed of carbon-rich rock, much like C-type (carbonaceous chondrite) asteroids, and ice. It is cratered, but the surface is noticeably smoother than that of Phobos, caused by the partial filling of craters with regolith. The two largest craters, Swift and Voltaire, measure about 3 kilometres across.

Orbital parameters

As seen from Mars, Deimos has an angular diameter of no more than 2.5' and therefore appears starlike to the naked eye. With a small telescope, a Martian observer can see Deimos' phases, which take 1.2648 days to run their course (Deimos' synodic period).

Unlike Phobos, which orbits so fast that it actually rises in the west and sets in the east, Deimos rises in the east and sets in the west. However, the orbital period of Deimos of about 30.4 hours exceeds the Martian solar day ("sol") of about 24.7 hours by such a small amount that it takes 2.7 days between rising and setting for an equatorial observer.

Because Deimos' orbit is relatively close to Mars and has only a very small inclination to Mars' equator, it cannot be seen from Martian latitudes greater than 82.7°.


Deimos is the location of Deimos Labs.


You can easily walk around Deimos in a day.

See also

  • Deimos - List of Deimos related articles.
  • Phobos - The other moon of Mars.