[FPSPACE] Lunar Topsy-Turviness

[Jens Kieffer-Olsen]

 It's common knowledge that the Moon is tidally locked
 to the Earth making its far side an enigma to mankind,
 until Russian scientists almost 50 years ago published
 photos taken by Luna 3 that revealed new craters, such
 as the one aptly named Циолковский  in honour of the
 visionary space age pioneer.

 However, a recent study points to the lunar farside
 having actually faced Earth a long time ago. But then
 a sudden switch-around occurred as a result of a hit
 from an asteroid.

 From Cosmos Online, January 2009
 
http://www.cosmosmagazine.com/news/2493/moons-backside-may-once-have-faced-e
arth
 we learn:

 [ ... ] new study, detailed this month in the journal
 Icarus, Wieczorek and Le Feuvre scoured images of the
 Moon's cratering patterns.

 Recent work has suggested that as the Moon orbits Earth,
 its leading side - the western hemisphere - is 30 per cent
 more likely to get hit by asteroids that the other. "It's
 really like a car moving through the rain, there'd be more
 rain falling on the front windscreen than the back,"
 explained Wieczorek.

 The researchers compared the ages of craters across the
 surface. As expected, that the younger asteroid impacts
 were on the western side. But to their surprise, the oldest
 craters were on the eastern side - the back windscreen -
 suggesting that the Moon's orientation may once have been
 reversed.

 The age of the craters was estimated by measured by looking
 at layers of debris thrown out from multiple impacts, and
 also by the number of craters superimposed on top of one
 another.

 But where's the evidence for a massive Moon-flipping
 asteroid impact? Wieczorek claims there are six giant
 basins that could mark the site of the blow. 

 The current favourite is the Smythii basin that lies on
 the Moon's equator "so it would have more ability to
 spin up the Moon than, say, if it was on the north pole."

 The experts estimates the direct hit at over 3.9 billion
 years ago.

--
Jens Kieffer-Olsen
Slagelse, Denmark