THE surface of the near-Earth asteroid Eros is unlike anything seen on the
Moon or other asteroids, data from NASA鈥檚 NEAR Shoemaker probe suggests.
Eros鈥檚 surface is covered by 40 to 50 metres of rock and dust left over from
collisions with other bodies, says Maria Zuber of the Massachusetts Institute of
Technology. Surprisingly, some of this rubble has slid downhill, apparently when
impacts shook the oblong asteroid.
As Zuber was describing her results last week, NEAR made its closest fly-by
to Eros so far, coming within 5 kilometres of the asteroid鈥檚 surface and sending
back the best pictures yet.
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Astronomers know that asteroids should accrete some rubble from
interplanetary space, but they have long debated how much. A few asteroids have
such low density that some researchers have suggested they are not solid bodies
at all, but loose agglomerations of rock. However, it now looks as if Eros was
part of something bigger, Zuber says. Like the most primitive meteorites, Eros
appears never to have melted, suggesting it is very old.
The landslides show up most clearly in Eros鈥檚 numerous craters, which contain
up to 100 metres of debris. Seismic shocks from 4.5 billion years of impacts may
have shaken some debris downhill.
Another surprise has been the discovery of millions of boulders between 10
and 20 metres across鈥攂igger than those found on the Moon. 鈥淭he boulders
have got to be coming from impacts,鈥� says Zuber, but it remains unclear why they
are breaking into house-sized objects. The fly-by also revealed boulders as
small as 1.4 metres.
