Far side of the moon once faced Earth before asteroid flipped it around.
By Daily Mail Reporter
Last updated at 3:15 PM on 22nd January 2009
The mysterious far side of the moon has long excited astronomers and science fiction writers alike because it never faces the Earth.But scientists now believe the moon may have faced the other way, before an asteroid flipped it around billions of years ago.
A study of impact craters suggests that our satellite performed the ultimate about-turn. Locked in synchronous rotation, the Moon never presents its far side to Earth. Dr Mark Wieczorek and Matthieu Le Feuvre, from the Paris Institute of Earth Physics, studied the age and distribution of 46 known craters.
Because it faces the direction of orbiting travel, the moon's western hemisphere should have more impact craters than its eastern hemisphere.
The French scientists found this was true of young craters, but older craters were mostly concentrated in the east. The implication was that the eastern face had once experienced more bombardment than the western face.
'This could be explained if a large asteroid impact had set the moon turning,' the New Scientist magazine reported.
'Such an impact would have put the satellite's rotation rate out of whack, so that for tens of thousands of years it would have appeared to slowly turn as viewed from Earth. Eventually, it would have settled into the current position.'
The far side of the moon, pictured from Apollo 11, was first seen by human eyes by the Apollo 8 crew in 1968
The moon now rotates once for every orbit it makes of the Earth. The far hemisphere was first photographed by the Soviet Luna 3 probe in 1959, and wasn't directly observed by human eyes until the Apollo 8 mission in 1968.
The face includes the largest known impact feature in the Solar System, called the South Pole-Aitken basin. It measures 1,550 miles in diameter and is 8 miles deep.
NASA gave MIT scientists the go-ahead in February 2008, to develop plans for a $1billion-plus array of radio telescopes that would be sited on the far side of the moon. These would be shielded from radio transmissions from Earth.
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