NASA's Hubble Space Telescope has observed a mysterious X-shaped debris pattern and trailing streamers of dust that suggest a head-on collision between two asteroids.

Astronomers have long thought the asteroid belt is being ground down through collisions, but such a smashup has never been seen before.

"This is quite different from the smooth dust envelopes of normal comets," said principal investigator David Jewitt of the University of California at Los Angeles. "The filaments are made of dust and gravel, presumably recently thrown out of the nucleus. Some are swept back by radiation pressure from sunlight to create straight dust streaks. Embedded in the filaments are co-moving blobs of dust that likely originated from tiny unseen parent bodies."

Hubble shows the main nucleus of P/2010 A2 lies outside its own halo of dust. This has never been seen before in a comet-like object. The nucleus is estimated to be 460 feet in diameter.

Normal comets fall into the inner regions of the solar system from icy reservoirs in the Kuiper Belt and Oort Cloud. As a comet nears the sun and warms up, ice near the surface vaporizes and ejects material from the solid comet nucleus via jets. But P/2010 A2 may have a different origin. It orbits in the warm, inner regions of the asteroid belt where its nearest neighbors are dry rocky bodies lacking volatile materials.

This leaves open the possibility that the complex debris tail is the result of an impact between two bodies, rather than ice simply melting from a parent body.

"This is a NASA Hubble Space Telescope picture a comet-like object called P/2010 A2, which was first discovered by the LINEAR (Lincoln Near-Earth Asteroid Research program) sky survey on January 6. The object appears so unusual in ground-based telescopic images that discretionary time on Hubble was used to take a close-up look. This picture, from the January 29 observation, shows a bizarre X-pattern of filamentary structures near the point-like nucleus of the object and trailing streamers of dust.

The inset picture shows a complex structure that suggests the object is not a comet but instead the product of a head-on collision between two asteroids traveling five times faster than a rifle bullet (5 kilometers per second). Astronomers have long thought that the asteroid belt is being ground down through collisions, but such a smashup has never before been seen. (Credit: NASA, ESA, and D. Jewitt (UCLA))"

Source: Space Telescope Science Institute