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View Diary: Back When the Earth Had Two Moons (67 comments)

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  •  I learned a different theory (5+ / 0-)

    The way I learned it in school was, the far side of the moon has more craters than the near side because most meteors heading towards the side that permanently faces the Earth, tend to hit the Earth. Meteors coming in from the far side have a clear shot. The thicker than average surface is due to all the meteoric bombardment, and the volcanism it caused (back in the days when the moon was still warm and smooshy inside, and could make volcanoes.)

    •  The earth isn't a big enough shield. (0+ / 0-)

      Remember the famous film of earthrise seen from the moon's orbit?  Note how small the Earth is in the moon's sky.  (It would only be about 4 times the full moon in earth's sky).  That isn't big enough to shield the near side of the moon from a large number of impacts.  As long as it comes in at any angle toward the moon other than from that one sector of sky where the earth is, it would still hit.  That's not enough to cause as drastic a difference as exists.  It should only make the near side about 10-15% less cratered than the far side if that was what was causing it - but the effect is far larger than that.

      •  Yeah, that's true (0+ / 0-)

        School was a long time ago. I guess we've improved our theories some since then. :) Thanks for explaining. I always love the science diaries here, good discussions with smart articulate people are fun.

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