[FPSPACE] Speaking of Apollo 15...

[LARRY KLAES]

Lunar Rock Pinpointed

When Apollo 15 landed on the outskirts of the Mare Imbrium basin,
astronauts gathered buckets full of rocks that later turned out to be
quite strange. The lander, it seemed, touched down in an anomalous region
of the Moon, one with a uniquely large concentration of radioactive
thorium, uranium, and potassium. Now astronomers on the ground have
identified a meteorite on Earth that they can trace directly to Imbrium.
As reported in the July 30th issue of SCIENCE, scientists deduced the
history of the 206-gram rock named Sayh al Uhaymir (SaU) 169 from its
radioactive markers. According to Edwin Gnos (Institute for Geological
Sciences, Bern, Switzerland) and colleagues, the makeup of the rock
suggests that it was involved in four different impact events that explain
the layered nature of the layered basin:

*First was the Imbrium formation event 3.9 billion years ago. This was the
origin of the rock material.
*2.8 billion years ago an impact south of Imbrium sent debris into the
basin, including SaU 169.
*A third impact at least 200 million years ago brought SaU 169 to the
surface (within a half meter).
*An impact less than 340,000 years ago launched SaU 169 on a course to
Earth. Its travel time was about 300,000 years.

> http://SkyandTelescope.com/news/article_1317_1.asp<http://skyandtelescopecom/news/article_1317_1.asp>

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