The far side of the moon may be the solid remains of a collision with a smaller companion moon, according to a study by planetary scientists at the University of California, Santa Cruz. The striking differences between the near and far sides of the moon have been a longstanding puzzle. The near side is relatively low and flat, while the topography of the far side is high and mountainous, with a much thicker crust.
The biggest hole in the solar system -- the South Pole-Aitken basin, is the largest known impact crater in the solar system, nearly 2,500 kilometers wide and 13 kilometers deep.
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