Original URL: http://www.theregister.co.uk/2010/09/17/lro_moon/

NASA reveals Moon's 'turbulent youth'

Quite a party, orbiter shows

By Lester Haines

Posted in Science, 17th September 2010 07:50 GMT

Data from NASA's Lunar Reconnaissance Orbiter (LRO) have revealed the Moon's "turbulent youth", during which it was pounded by "two distinct populations of asteroids or comets".

The agency has put together a "detailed global topographic map" of our satellite, captured by the LRO's Lunar Orbiter Laser Altimeter (LOLA), showing how an early large-fragment bombardment of the surface was followed by an assault by relatively small objects. It includes this view* of the Moon "from the vantage point of the eastern limb":

NASA Lunar Reconnaissance Orbiter image of the Moon

As James Head of Brown University puts it in the latest edition of Science: "Our new LRO LOLA dataset shows that the older highland impactor population can be clearly distinguished from the younger population in the lunar 'maria' - giant impact basins filled with solidified lava flows.


LOLA has also enabled Head to estimate just when the big rocks stopped falling. He elaborates: "Using the crater counts from the different impact basins and examining the populations making up the superposed craters, we can look back in time to discover when this transition in impactor populations occurred. The LRO LOLA impact crater database shows that the transition occurred about the time of the Orientale impact basin, about 3.8 billion years ago.


All of this crater-gazing could prove significant for studies as to how our own planet suffered at the hands of comets and asteroids. While there is evidence of this pounding - such as the "110-mile-diameter, partially buried crater at Chicxulub, in the Yucatan Peninsula of Mexico", resulting from a significant hit 65 million years ago - most of the scars have long since disappeared.

The Moon, free of erosion and other crater-wiping factors, is "analogous to a Rosetta stone for understanding the bombardment history of the Earth", Head explained.


Head's study in Science is accompanied by two further papers the findings from LRO's Diviner Lunar Radiometer Experiment, demonstrating that "the geologic processes that forged the lunar surface were complex as well". NASA has more here. ®



