[meteorite-list] Lunar Crater Stats Indicate Hidden Population of Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 5 Aug 2009 15:30:01 -0700 (PDT)
Message-ID: <200908052230.n75MU13W012014_at_zagami.jpl.nasa.gov>

http://www.technologyreview.com/blog/arxiv/23878/

Lunar Crater Stats Indicate Hidden Population of Asteroids
Technology Review
August 3, 2009

The asymmetric distribution of craters on the Moon may have been caused
by an undiscovered population of near Earth asteroids

Many moons are locked in synchronous rotation with their mother planets.
Examples include the Galilean moons of Jupiter, Neptune's moon Triton
and our own Moon.

In the 80s and 90s astronomers noticed that the distribution of craters
on these objects was asymmetric: they were more heavily cratered on
their leading hemispheres which makes sense since it seems obvious that
these areas should be struck more often.

It wasn't until 2003, however, that the same asymmetric crater
distribution was measured on our Moon. Now Takashi Ito at the National
Astronomical Observatory in Japan and Renu Malhotra at the University of
Arizona have asked an interesting question. of the data. Can the
asymmetric distribution of craters on the Moon be explained by the known
distribution of near Earth asteroids that are thought to have caused
them? Their answer is a cautious "no".

To properly explain the crater distribution, Ito and Malhotra say some
other factor must have been involved. One possibility is that we simply
haven't seen all the craters yet: the ongoing lunar mapping missions may
help on that score.

Another idea is that the Earth's tidal forces tear Earth-crossing
asteroids apart, creating a higher number of impacts than might
otherwise be expected.

But the most exciting and potentially worrying possibility is that there
exists a previously unseen population of near Earth asteroids that orbit
the Sun at approximately the same distance as the Earth. These have gone
unnoticed because they are smaller or darker than other asteroids, say
Ito and Malhotra.

"More complete observational surveys of the near-Earth asteroids can
test our prediction," they say.

And let's not waste too much time about it. By some reckonings, asteroid
impacts represent the greatest threat to humankind that we are able to
calculate.

Ref: arxiv.org/abs/0907.3010 <http://arxiv.org/abs/0907.3010>:
Asymmetric Impacts of Near-Earth Asteroids on The Moon
Received on Wed 05 Aug 2009 06:30:01 PM PDT