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Why are there more maria on the near side of the Moon?

My astronomy instructor said that there are more maria on the near side of the Moon than there are on the far side of the Moon. Is this true and if so why? If they were created by asteroid collisions, would there not likely be more on the far side of the moon, away from the earth than on the side that faces the Earth, since the far side is not blocked by the Earth?

Yes, the craters on the Moon were created by impacts from meteorites. It is thought that tidal effects have caused the crust of the Moon to be thinner on the "Earthward side". During the formation of the Moon, lava flows were able to move through this thinner crust and flood the basins on the near side, but not as much on the far side of the Moon. The areas of these lava flows are what we now call maria, which is Latin for "seas".

November 2003, Brian Kent (more by Brian Kent) (Like this Answer)

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