spacetoday.net: Second moon may explain lunar farside

Posted: Thu, Aug 4, 2011, 7:10 AM ET (1110 GMT)
Second moon impacting the Moon (UCSC)

The impact of a second moon with the Earth's Moon may explain why the far side of the Moon is so mountainous, scientists reported this week. In a paper published in the latest issue of the journal Nature, scientists used computer models of the Moon's formation to offer a potential explanation of the lunar farside, which is dominated by mountain ranges and cratered highlands, unlike the side of the Moon that faces the Earth. The models, which explain the Moon's creation through the collision of a Mars-sized protoplanet with the early Earth, show that a second, smaller object is also created in a similar orbit. In those models, the smaller object collides at relatively low speeds with the Moon, covering that hemisphere with a layer of rock tens of kilometers thick. This "big splat" model could be tested in data collected by future missions to the Moon, including those that return samples from the lunar farside.