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Old Oct 4 2009, 05:41 AM   #6
Master Sneak
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Join Date: Apr 2007
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Default Re: New Messenger images of Mercury

We do, but the Earth has a thick atmosphere which conveniently burns up the small ones (see the other thread about the Perseid meteor shower). The larger ones still create craters on the surface of the Earth (see Meteor Crater in Arizona), but they are gradually eroded away over millions of years by wind and water.

Each planet has a different bombardment history, depending on its size and location in the Solar System. Jupiter is probably the most bombarded planet because of its gravity, but its atmosphere is so thick any impacts only leave traces for a few days or weeks (e.g. the Comet Shoemaker Levy 9 impact).

Because the Moon is close to the Earth it has had roughly the same bombardment history. It's sobering to think that all the impacts which created the craters on the Moon, including the gigantic collisions which carved out the lunar maria, also happened here on the Earth. Thankfully it was all a long time ago. Our friend Jupiter has cleared up much of the crud floating about the Solar System, so these huge impacts don't happen anywhere near as frequently as they used to.
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