![]() ![]() These findings have prompted some investigators to suggest that the cavities in Phobos may contain large volumes of various ices, but this is difficult to demonstrate since no evidence of hydration of Phobos’ outer layers has been found. Moreover, studies have also shown that Phobos is extremely porous, and that large internal cavities (or voids), account for about 25-35% of the moon’s total volume, which argues against an asteroidal origin. In fact, Infrared studies of Phobos have shown that the body is a carbon-poor rubble pile that is only loosely held together by a thin crust of mainly regolith. However, since Deimos’ orbits is very close to Mars, and has a very small inclination with respect to Mars’ equatorial plane, an observer on Mars would not be able to see Deimos from Martian latitudes greater than 82.7 degrees.ĭeimos’ orbit is progressively getting bigger, since at its distance from Mars, the planet’s gravitational influence is not strong enough to prevent tidal acceleration of the moon, and most investigators believe that Deimos will eventually escape Mars’ gravity altogether.Īlthough Phobos is substantially bigger than Mar’s other moon, Deimos, it is not massive enough for its own gravity to form into a spherical shape, or for its gravity to hold onto an atmosphere of any sort. However, since the moon’s Sun-synodic orbital period of 30.4 hours is slightly longer than a Martian day (“sol”), which is 24.7 hours long, 2.7 Martian days would elapse between each successive rising and setting of the moon for an observer on Mars’ equator. In terms of its composition, Deimos is made from rock that is rich in carbonaceous material, and while it is heavily cratered, most of its surface irregularities have been smoothed over by a thick layer of highly porous regolith.Īs seen from the surface of Mars, Deimos rises in the east, and sets in the west. Investigations are, however, continuing.ĭeimos closely resembles C or D-type asteroids in terms of its spectrum, albedo (reflectivity), and overall geometry in the sense that it is highly non-spherical having dimensions of 15 × 12.2 × 11 km. While the latter hypothesis appears to be the most likely, it does not explain why the putative ring of debris formed into two bodies, or why they have such disparate distances from Mars. According to this proposed scenario, the collision could very well have created a ring of debris around Mars, which subsequently coalesced into the two moons we observe today. One other hypothesis holds that both moons were created when a body with about one third the mass of Mars collided with it, which seems probable given that the crust in parts of Mars’ northern hemisphere is markedly thinner than in the southern hemisphere. ![]() Moreover, while atmospheric drag or tidal forces could have circularized the orbits of both moons, several studies suggest that the solar system is not old enough for this to have happened. While the composition of Deimos (but not that of Phobos) shows remarkable similarities to C and D-type asteroids that inhabit the main asteroid belt, both moons nevertheless have masses that would have made it impossible for the thin atmosphere of Mars to slow the objects down sufficiently for the planet’s gravity to have captured them. The first hypothesis holds that both moons were captured by Mars after their orbits in the main asteroid bet were disturbed by a mechanism that is yet to be explained. ![]() The origin of both of Mars’ moons is still unknown, although there are two controversial hypotheses that could help explain how they came about. Generally, though, Phobos cannot be spotted with modest or even medium-sized amateur equipment. Nevertheless, Mars outshines its closest moon by at least 200,000 times, making it necessary to construct an occulting bar (to mask out Mars’ light) on a very large telescope under very dark skies in order to have even a small chance of spotting Phobos even at maximum elongation (maximum possible distance away) from Mars. While Deimos can sometimes be seen in large amateur telescopes, spotting Phobos, on the other hand, is another matter entirely, although the chances of doing so improve somewhat when Mars is closest to Earth. Phobos is named after the Greek god of horror and fear, while his twin brother Deimos is named after the the god of terror, both of whom accompanied their father the war god Ares into battle alongside his sisters the war goddess Enyo, and Eris, the goddess of discord.
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