Unfamiliar sight: The far side of the Moon as captured by one of NASA's Apollo missions in the 1970s. The Moon is locked in a synchronous rotation with the Earth, meaning that we always see the same side of it.
Credit: NASA
This about-turn could also mean a major rethink about how Moon craters are aged. Previous estimates have assumed asteroid impacts were totally random, but if the forwards impact effect holds true, and then the Moon flipped, many old measurements will now be inaccurate, the researchers said.
"It seems plausible that the Moon was originally orientated in the opposite direction to what we see today," commented Katherine Joy, a lunar geologist from University College London in England.
Major rethink
This discovery also "has important consequences for understanding the impact cratering record in the whole of the inner Solar System… cratering age calculations may have a new degree of ambiguity," she said.
"This is the first real evidence that [a Moon flip] could have occurred," added planetary geophysicist Jay Melosh from the University of Arizona in Tucson; the expert who first came up with the theory in 1975.
The find also raises the prospect that other satellites in our Solar System might have flipped too, said Melosh. "The moons of Saturn and Jupiter currently face their primary direction, but they may have undergone reversal at some point."
The next stage will be finding more craters to back up Wieczorek's findings, and the answers may not be far away – Indian and Japanese Moon probes currently in orbit and the U.S.'s GRAIL (Gravity Recovery and Interior Laboratory) mission, slated for launch in 2011, could uncover vital new evidence for the about-turn.
Moon's backside may once have faced Earth
We were mooned!