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Martian Moons




Phobos (fear) Deimos (panic)

Phobos
(fear)

Deimos
(panic)

PHOBOS AND DEIMOS
(moons of Mars)

Mars has two small moons: Phobos and Deimos. Phobos (fear) and Deimos (panic) were named after the horses that pulled the chariot of the Greek war god Ares, the counterpart to the Roman war god Mars. Both Phobos and Deimos were discovered in 1877 by American astronomer Asaph Hall. The moons appear to have surface materials similar to many asteroids in the outer asteroid belt, which leads most scientists to believe that Phobos and Deimos are captured asteroids.


This animation shows Phobos as a large white dot against a black background, representing Phobos, moving from the lower center toward the upward right corner. Above and to the left of it is Deimos, a smaller white dot, that also moves upward and to the right but at a much slower pace. In fact, Phobos starts out below Deimos, the smaller dot, and quickly moves past it in the sequence. This animation shows a large white dot against a black background, representing Phobos, moving from the lower center toward the upward right corner. Above and to the left of it is a smaller white dot, representing Deimos, that also moves upward and to the right but at a much slower pace. In fact, Phobos starts out below Deimos and quickly moves past it in the sequence. In the lower right quadrant, a small square insert shows an oblong, potato-shaped object, white against a black background, representing Phobos, with the upper right limb missing. The right side is also partially obscured by darkness. At the top of the image, the stars of the constellation Sagittarius are labeled, counterclockwise from upper left: Kaus Australis, Alnasl, Kaus Meridionalis, Kaus Borealis, Phi Sgr, and Nunki. This image shows on the upper right side, is a small white circle against a black background representing Phobos, with a smaller black circle representing Deimos a little above and to the right of it. This image shows a large white circle representing an enhanced image of the light from Phobos with an oblong rock-like object representing Phobos itself inserted in the middle. A little above and to the right of that is a smaller white circle representing Deimos. In the lower left corner are several white pinpoints labeled 'The Pleiades.'
Two Moons Passing
in the Night
Two Moons and the
Pleiades from Mars
 
This sequence of images shows the rough outline of Phobos, fuzzy on the left, becoming gradually sharper in two successive images to the right. The fourth image, on the far right, is a much closer image taken from orbit around Mars by the Mars Express. It shows a bumpy, crater surface, with a circular portion missing from the upper right limb.
Phobos Viewed from Mars

See the Spirit Press Release for additional information.


Quick Facts about Phobos and Deimos

  Phobos Deimos
Mean distance from Mars (km) 9377 23436
Orbital period (Mars days) 0.31891 1.26244
Major axis (km) 26 16
Minor axis (km) 18 10
Mass (x 1015 kg) 10.8 1.8
Mean density (kg/m3) 1900 1750

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