The Dark Side of The Moons

Aert van der Neer  (c. 1603 – 1677)

For decades, scientists have been trying to understand why the near side of the Moon – the one visible from Earth – is flat and cratered while the rarely-seen far side is heavily cratered and has mountain ranges higher than 3,000m.

Various theories have been proposed to explain what’s termed the lunar dichotomy. One suggests that tidal heating, caused by the pull of the Earth on the ocean of liquid rock that once flowed under the lunar crust, may have been the cause.
But a new paper proposes a different solution: a long-term series of cosmic collisions.

The researchers argue that the Earth was struck about four billion years ago by another planet about the size of Mars. This is known as the global-impact hypothesis. The resulting debris eventually coalesced to form our Moon.

But the scientists say that another, smaller lunar body may have formed from the same material.
After spending millions of years “stuck” in a gravitational tug of war between the Earth and the Moon, the smaller moon embarked on a collision course with its big sister, slowly crashing into it at a velocity of less than three kilometres per second – slower than the speed of sound in rocks.
Dr Martin Jutzi from the University of Bern, Switzerland, one of the authors of the paper, explained, “It was a rather gentle collision … that’s important because it means no huge shocks or melting was produced.
The bigger moon would have had a “magma ocean” with a thin crust on top, and the impact would have led to the build-up of material on the lunar crust and would also have redistributed the underlying magma to the near side of the moon, an idea backed up by observations from Nasa’s Lunar Prospector spacecraft.

Scientists would like to get their hands on samples from the far side of the Moon to prove their theory.

http://www.bbc.co.uk/news/science-environment-14391929

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