Scientists believe the images represent an extremely recent asteroid collision, with a small rock, perhaps 10-15 feet wide, colliding with a larger, roughly 400-foot-wide one. When they first sighted the image in January, researchers thought the collision had just occurred, but now they date it to early 2009.
"We expected the debris field to expand dramatically, like shrapnel flying from a hand grenade," said astronomer David Jewitt of the University of California in Los Angeles, who is a leader of Hubble observations
. "But what happened was quite the opposite. We found that the object is expanding very, very slowly."
The peculiar object, dubbed P/2010 A2, was found cruising around the asteroid belt, a reservoir of millions of rocky bodies between the orbits of Mars and Jupiter. It is estimated modest-sized asteroids smash into each other about once a year. When the objects collide, they inject dust into interplanetary space. But until now, astronomers have relied on models to make predictions about the frequency of these collisions and the amount of dust produced, said NASA this week
It is rare for NASA to photograph colliding asteroids because large impacts are rare and faint smaller impacts like the one that produced this comet formation are hard to detect.
The Hubble images
, taken from January to May 2010 with the telescope's Wide Field Camera 3, reveal a point-like object about 400 feet wide, with a long, flowing dust tail behind a never-before-seen X pattern. Particle sizes in the tail are estimated to vary from about 1/25th of an inch to an inch in diameter.
The 400-foot-wide object in the Hubble image is the remnant of a slightly larger precursor body. Astronomers think a smaller rock, perhaps 10 to 15 feet wide, slammed into the larger one. The pair probably collided at high speed, about 11,000 mph, which smashed and vaporized the small asteroid and stripped material from the larger one. Jewitt estimates that the violent encounter happened in February or March 2009 and was as powerful as the detonation of a small atomic bomb, reports NASA.
After using Hubble to track
the oddball body for five months, astronomers were surprised to find that they had missed the suspected smashup by a year. The science results are reported in the October 14 issue of the science journal Nature.