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Deimos and Phobos







Orbit: 23,459 km from Mars
Orbital period: 30 hours
Gravity: 0.003 m/s²
Circumference: 39 km
Diameter:  4800 km
Mass: 1.08e23 kg

Deimos is the smallest of Mars' two moons

Deimos (“DEE mos”) is the smaller and outermost of Mars’ two moons. It is one of  the smallest known moons in the solar system. In Greek mythology, Deimos is one of the sons of Ares (Mars)       and  Aphrodite (Venus); “deimos” is Greek for “panic”. Discovered 1877 August 12 by Hall, photographed  by  Viking 1 in 1977.



Orbit: 9,378 km from Mars
Orbital period: 8 hours
Gravity: 0.0057 m/s²
Circumference: 70 km
Diameter:  22.2 km
Mass: 1.08e16 kg
Phobos moon

Deimos and Phobos are composed of  carbon-rich       rock like C-type asteroids and ice.       Both are heavily cratered. Deimos and Phobos are probably        asteroids      perturbed       by        Jupiter into orbits that allowed them to be  captured by Mars. Phobos (“FOH bus”) is the larger and innermost of Mars’ two moons.       Phobos  is closer to its primary than any other moon in the solar system,       less  than 6000 km above the surface of Mars.  It       is also one of the smallest moons       in the solar system. In Greek mythology, Phobos is one of the sons of Ares (Mars) and        Aphrodite (Venus).       “phobos” is Greek for “fear” (the root of “phobia”).  Discovered 1877 August 18       by Hall;  photographed by        Mariner 9 in 1971,         Viking 1 in 1977, and        Phobos in 1988. Phobos orbits Mars below the  synchronous orbit radius.  Thus it rises in the west,       moves very rapidly across the sky and sets in the east, usually twice a  day.       It is so close to the surface that it cannot be seen above the  horizon       from all points on the surface of Mars. And Phobos is doomed:  because its orbit is below synchronous altitude       tidal forces are lowering its orbit       (current rate: about 1.8 meters per  century).       In about 50 million years it will either crash onto the surface  of Mars       or (more likely) break up into a ring.      (This is the opposite  effect to that operating to raise the orbit of   the Moon.) Phobos and Deimos may be composed of  carbon-rich       rock  like C-type asteroids.       But their densities are so low that they cannot be pure rock.       They are more       likely composed of a mixture of rock and ice.       Both  are heavily cratered.    New images from Mars Global Surveyor indicate that  Phobos is covered with a layer of fine dust about a meter thick, similar to the  regolith on the Earth’s Moon. Phobos taken from Soviet spacecraft The Soviet spacecraft Phobos  2 detected a faint but steady       outgassing from Phobos.        Unfortunately, Phobos 2 died before it could determine the nature of the        material; water is the best bet. Phobos 2 also returned a few images (right). The most prominent feature on Phobos is the large crater named Stickney,       the maiden name of Hall’s wife (above).       Like Mimas’ crater Herschel (on a smaller scale)       the  impact that created Stickney must have almost shattered Phobos. The        grooves and streaks on the surface were probably also caused by the        Stickney impact. Phobos and Deimos are widely believed to be captured        asteroids.  There is some speculation that       they  originated in the outer solar system rather than in the main asteroid belt. Phobos and Deimos may someday be useful as “space stations” from which to  study       Mars or as intermediate stops to and from the Martian surface;  especially if       the presence of ice is confirmed.

Deimos and Phobos

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