Sunlight makes asteroids binary system A new study puts solar
spin on asteroids, their moons and Earth impacts. July 9, 2008
Provided by the University of Maryland, College Park July 9,
2008 This image shows the asteroid Ida, on the left, and its
moon Dactyl. Photo by NEAR/JPL/NASA Asteroids with moons, which
scientists call binary asteroids, are common in the solar
system. A longstanding question has been how the majority of
such moons are formed. In this week's issue of the journal
Nature, a trio of astronomers from Maryland and France say the
surprising answer is sunlight, which can increase or decrease
the spin rate of an asteroid. Derek Richardson, of the
University of Maryland, his former student Kevin Walsh, now
Poincare Fellow in the Planetology Group in the Cassiopee
Laboratory of CNRS at the Cote d'Azur Observatory, France, and
that group's leader, coauthor Patrick Michel outline a model
showing that when solar energy spins up a rubble pile asteroid
to a sufficiently fast rate, material is slung off