Asteroid families more common than believed

By James Maynard , Jun 02, 2013 07:30 PM EDT

Asteroids travel in families, and there are more of them than we thought, according to new measurements from NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft.

Asteroid families are occasionally formed when two asteroids collide. Fragments of the bodies can travel along with one or both of the asteroids through space, creating such a grouping. As time goes on, these families slowly drift apart. Some of these can head toward the Earth, with potentially catastrophic results.

The smaller pieces of stone are generally made of the same materials which compose their parent body. Detecting the makeup of these small objects can be difficult in visible light, but the infrared cameras of the WISE spacecraft made that task easier.

"We're separating zebras from the gazelles. Before, asteroid family members were harder to tell apart because they were traveling in nearby packs. But now we have a better idea of which asteroid belongs to which family," Joseph Masiero of NASA's Jet Propulsion Laboratory, lead author of the study, said.

When images from NEOWISE, the tools aboard the WISE spacecraft meant to discover new asteroids, was examined, researchers discovered 28 new families of asteroids. Thousands of previously-identified asteroids were classified into families for the first time.

Most asteroids stay in stable orbits, mainly between the orbits of Mars and Jupiter, but collisions can send some of these boulders heading on a collision course with Earth. Any such asteroid which travels within 28 million miles of our home world is considered a Near-Earth object, or NEO.

"NEOWISE has given us the data for a much more detailed look at the evolution of asteroids throughout the solar system. This will help us trace the NEOs back to their sources and understand how some of them have migrated to orbits hazardous to the Earth," Lindley Johnson, program executive for the Near-Earth Object Observation Program at NASA Headquarters in Washington, said.

The space observatory took millions of individual images of bodies in the asteroid belt. Masiero's team studied 120,000 of these objects, around one-fifth of the 600,000 known asteroids. Researchers were able to assign about 38,000 of these bodies to families. Where there had only been 48 recognized families of asteroids before the new WISE survey, that list of family names had to be expanded to 76 when research was complete.

The WISE spacecraft was put into hibernation mode in 2011 after photographing the entire sky twice.

The new study appears in the Astrophysical Journal.

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