On Earth, in every crater there's usually at least some remnant of a meteorite. But with all the craters on the Moon, where are the meteorites in the middle of them?


1 Answer 1


All over the place

But as the whole surface of the Moon is either rock, or rock broken by meteor impacts, or meteors, it becomes very difficult to identify them.

Moon meteorites will have none of the classic attributes that make Earth meteorites easily identifiable.
For example, one way to identify meteorites on Earth is by the classic surface melt and ablation effect caused by atmospheric entry. This would be completely absent on Moon meteorites, because no atmosphere.
Another way to identify a potential meteorite on Earth is, indeed, to look in its crater, or to follow a report of an impact. On the Moon there are untold numbers of craters, and very, very few locals to report an impact.

And even if you do locate a likely rock: how to you verify it to be a meteorite, not a Moon rock?

  • Both moon rocks and meteors have been exposed to vacuum of space only, for extended periods.
  • Both have experienced similar thermal cycles from sunlight.
  • Both have been in similar radiation environments.
  • Both will have a complete absence of organic matter.
  • Both will have physical evidence of violent mechanical shock.

It would require a very detailed analysis of a given rock, to determine things such as the average distance from the Sun over the last billion years, or exact isotope ratios that show where/when in the primordial solar system the rock formed, to verify if a Moon rock is a meteorite or a meteowrong.

But we know that all, or at least the extreme majority of Moon craters are not volcanic/geological in origin, but were created by impacts. And the Moon has craters over craters within craters overlapping craters. And smaller craters in them, and microcraters in the dust. Trillions of them, of all scales.

The Earth collects some 5000 tons of meteors and meteordust per year, but the surface weathering eats them up. A similar proportionate amount would hit the Moon, but there is no weathering to absorb the meteorites. If only one micrometer of meteordust settles on the Moon in a million years, the moon will still have a layer 4.5 millimeters thick of just meteors.(moon age 4.5 billion years).

So, when is a bit of meteordust that lies on the surface of the Moon a Meteor, and when is it part of Moon regolith, simply because it has been there for 4 billion years and is claiming squatter's rights?


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