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Ceres lacks large craters

The uncertainty of science: Using data from Dawn, scientists have found that the solar system’s largest asteroid, Ceres (also called a dwarf planet by confused scientists), has a mysterious lack of large craters.

Marchi and colleagues modeled collisions of other bodies with Ceres since the dwarf planet formed, and predicted the number of large craters that should have been present on its surface. These models predicted Ceres should have up to 10 to 15 craters larger than 250 miles (400 kilometers) in diameter, and at least 40 craters larger than 60 miles (100 kilometers) wide. However, Dawn has shown that Ceres has only 16 craters larger than 60 miles, and none larger than 175 miles (280 kilometers) across.

They postulate two theories to explain the lack. First, Ceres might have formed far out beyond Neptune, though this theory is not favored because some models still say that even here Ceres should have large craters. Second,

One reason for the lack of large craters could be related the interior structure of Ceres. There is evidence from Dawn that the upper layers of Ceres contain ice. Because ice is less dense than rock, the topography could “relax,” or smooth out, more quickly if ice or another lower-density material, such as salt, dominates the subsurface composition. Recent analysis of the center of Ceres’ Occator Crater suggests that the salts found there could be remnants of a frozen ocean under the surface, and that liquid water could have been present in Ceres’ interior.

Past hydrothermal activity, which may have influenced the salts rising to the surface at Occator, could also have something to do with the erasure of craters. If Ceres had widespread cryovolcanic activity in the past — the eruption of volatiles such as water — these cryogenic materials also could have flowed across the surface, possibly burying pre-existing large craters. Smaller impacts would have then created new craters on the resurfaced area.

This theory doesn’t really work that well either, because it fails to explain why only the big craters got erased.

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2 comments

  • Tom Billings

    “This theory doesn’t really work that well either, because it fails to explain why only the big craters got erased.”

    Actually, it may, in a way that gives more clues about the depth of the ice/rock combo over the underground ocean. Larger craters, in general, will be deeper craters. If the craters are filled in when their bottom-most portions leak liquid water from the underlying ocean, and pressure from the rest of the lithoshpere forces that water at a bit of pressure into the crater, then we may have an indicator of the depth of the lithosphere covering the ocean.

    Basically, what is the deepest surviving crater on Ceres?

    That is the minimum depth of the lithosphere covering Ceres’ ocean.

    It’s probably a bit more, because the pressure from the rest of the lithosphere forcing water through cracks will allow filling when there is no complete breakthrough. At some point the thickness remaining will be enough that even water forced up through cracks will refreeze before it fills a crater, and you will have a surviving crater.

  • Localfluff

    And Pluto lacks small craters, if I understand it correctly, with no good explanation yet. Next up is a place which has only large and small craters, no medium sized. Celestial worlds are like individuals in that they become unique with age.

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