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Study: Why the Moon's Far Side Looks So Different
StartsWithABang writes 55 years ago, the Soviet probe Luna 3 imaged the side of the Moon that faces away from us for the first time. Surprisingly, there were only two very small maria (dark regions) and large amounts of mountainous terrain, in stark contrast to the side that faces us. This remained a mystery for a very long time, even after we developed the giant impact hypothesis to explain the origin of the Moon. But a new study finally appears to solve the mystery, crediting the heat generated on the near side from a hot, young Earth with creating the differences between the two hemispheres.
But really, did the earth stay hot enough for "a few million years" - hot enough to affect the locked side of the moon more than the other?
The moon has no atmosphere, thus radiation from the earth cannot affect the far side of the moon at all. So obviously, even to this day, the earth still affects "the locked side of the moon more than the other". The question is simply how much. The moon and earth were both molten after the collision, so it was not a matter of the earth being hot enough to melt the moon, but merely the earth imparting energy to prolong the cooling of the near side. No matter what, the near side must have cooled slower than the far side - it's a straightforward matter of thermodynamics. One side of the moon was receiving energy from the earth while the other side was not. The near side didn't need to stay so hot it was incandescent, but merely "softer" so that small impacts would heal more on the near side than the far side, and the duration only needed to be long enough to result in some degree of visible difference, which is what we still see today.
The whole thing sounds plausible to me.
Better known as 318230.
Earth is 12,742 km in diameter. The moon is 363,104 km, 28.5 diameters, away at perigee, and 405,696 km, 31.8 diameters, at apogee.
In round numbers the moon is 30 Earth diameters away.
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