Phobos and Deimos: An origin story

MMX will help answer where the two tiny moons came from

There are traditionally two theories about where the Martian moons came from. One suggests that both moons are merely captured asteroids. The albedo (reflectivity) of Phobos supports this. “The albedo of Phobos is very low, making the moon very dark,” says Tasker. “Examination of the wavelengths of reflected light from Phobos gives a result very similar to that of [low-albedo] asteroids.” This suggests the moons may have initially formed in the main asteroid belt between Mars and Jupiter and were later snagged by Mars's gravity to become captured moons. The idea that Phobos and Deimos are two halves of a trapped comet is a twist on this theory. However, Phobos and Deimos orbit Mars's equator in a very circular path. “This is hard to achieve with capture,” says Tasker, “but…

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BBC Sky at Night United Kingdom (Digital) - 1 Issue, September 2024

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