Is there evidence of Earth meteor impacts on the moon?

07 August 2011

Question

Dear the Naked scientists,
My question is really quite a simple one. I understand that in some of the larger historical meteorite strikes on Earth that they were sufficiently energetic that some matter achieved escape velocity and if that's true, did the moon capture any of this matter and is there any detectable evidence of these impacts on the moon?

Cheers,
Matt Lewis (UK).

P.S. Great show! Love it! :)

Answer

Dominic - You're absolutely right that most impacts of bodies onto a planet will give a lot of material escape velocity, and that material will be lost as debris to space. And so, there's a lot of debris out there in the solar system and the chances are that it will, within a few million years, collide with one of the planets. Now, if you've got bodies colliding with the Earth then statistically, that material is quite likely to end up on the moon simply because the moon is the closest body to us. It's only 400,000 kilometres away, about a hundred times closer than the next nearest object which would be Mars.

The problem would be actually identifying individual features on the Moon as being from meteor impacts from material coming from the Earth. If you just look at a crater, all you can say is that material of such and such a mass has impacted the Moon, you have to actually find the meteorite and recover it to start doing chemical analysis on that to work out where it come from. For example, if you can find trapped gases in there, you can try and match it against the atmosphere of one of the planets.

The Moon has no atmosphere and that means these meteorites will get quite a hard impact onto the surface and they will probably be totally vaporized in the impact - unlike, for example, a meteor impact on the Earth or Mars which is cushioned by the atmosphere and so, those objects can survive and be found.

Also of course, we haven't explored very much of the Moon's surface in comparison to Mars where we've had rovers roving the surface for the last 6 years or so, finding, say, dozens of meteorites on the surface of Mars. So we haven't really explored enough to find meteorites from the Moon even if they were there. So I think you'd be lucky to find them.

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