A peculiar object just discovered beyond the orbit of Mars could be the survivor of an asteroid collision. Researchers haven't yet confirmed the idea, but further studies should produce new clues about the composition and behavior of these tiny rocky bodies--information that someday could help prevent a catastrophic collision with Earth.
Billions of asteroids and comets are whirling around the sun, and they have their own distinct traffic patterns. Most asteroids, which are made of rock, confine themselves to a belt between the orbits of Mars and Jupiter. Most comets, which consist of water ice, linger at the far reaches of the solar system. A few comets have fallen into arcs that take them periodically close to the sun, where their spectacular tails form, as solar heat vaporizes some of their ice.
Last month astronomers spotted something that didn't fit either category. The object, dubbed P/2010 A2, orbits the sun well within the main asteroid belt, according to observations taken as part of the Lincoln Near Earth Asteroid Research sky survey. Unlike its conventional rocky cousins, however, this object is sporting what looks like a tail.
To find out what was going on, a team trained the Hubble Space Telescope's camera on P/2010 A2 on 25 and 29 January. The results suggest that the object's tail is rubble from a crash with another asteroid, not the sign of a wayward comet. Unlike every other comet that's ever been observed, the object's 140-meter-wide nucleus sits off-center from the tail (see photo). The tail features an x-shaped pattern--again, something unknown among comets--and so far shows no signs of ice.
The tentative verdict is that this probably is the remnant of a recent asteroid collision, where a smaller body struck a larger object at a velocity of about 15,000 kilometer per hour. The team, led by astronomer and lead investigator David Jewitt of the University of California, Los Angeles, announced their conclusion yesterday.
Astronomer Peter Brown of the University of Western Ontario in Canada agrees. "This is clearly something unusual and not typical of the sort of behavior we expect from a common comet," says Brown, who was not involved in the study. Astronomer William Bottke of the Southwest Research Institute in Boulder, Colorado, says the researchers need to collect more data about the object's composition, so they can "put the collision into context."
If P/2010 A2 is the result of a collision, Jewitt says, further observations will improve understanding of the physics of the impact. And collecting real data, he says, might help scientists learn how to destroy an incoming asteroid that threatens Earth. "That's not why I care about the object," he says, "but this is a real connection."
