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Martian Moons May Have Formed Like Earth's

Posted by Soulskill on from the carved-out-of-green-cheese dept.

sciencehabit writes: Astronomers have long believed that Mars snatched its two moons — Phobos and Deimos — from the asteroid belt. That would explain why the objects look like asteroids—dark, crater-pocked, and potato-shaped. But computer simulations by two independent teams of astronomers (abstract 1, abstract 2) indicated that Mars's moons formed much like ours did, after a giant space rock smashed into the planet and sprayed debris into orbit.

3 of 50 comments (clear)

  1. Re:Wou would have thought. by Vulch · · Score: 3, Interesting

    Basically you need a third object to get involved, for instance it's thought that Triton was one of a pair of similar sized objects in orbit around each other. Triton was (relatively) going backwards at the time of a close approach so landed up in orbit around Neptune, it's partner got slung away. That also seems to explain why Triton is in a retrograde orbit.

  2. Density matches theory by Yergle143 · · Score: 3, Interesting

    Here are some relevant space object mean densities. Mars 3.93 g/cm3, Phobos 1.87 g/cm3, Deimos 1.47 g/cm3, Mercury 5.42 g/cm3, Luna 3.34 g/cm3, Earth 5.51 g/cm3, Ceres 2.07 g/cm3, Vesta 3.45 g/cm3, Europa 3.01 g/cm3, Comet 67P/Churyumov–Gerasimenko 0.47 g/cm3. If Phobos and Deimos formed from a violent collision it might be expected that they would be dense rocky objects like our moon or Vesta. However it seems that these moons more resemble the icy object end of the density spectrum. Did they form during a wetter Martian era?
    I think the take home message is that some exploring of the Martian moons is in order; a sample return mission would be much simpler than a Mars return with an interesting scientific purpose.
     

    1. Re:Density matches theory by ceoyoyo · · Score: 3, Interesting

      The impact hypothesis nicely explains why the moon is less dense than Earth: the impact preferentially threw up light elements from the crust and upper mantle, not heavy elements that would have sunk to the core. The densities of Phobos and Deimos are also less than that of Mars, but because they're so small, and are probably more like orbiting gravel piles, their densities are also consistent with small asteroids.