Jul 26, 2013 02:03 PM EDT By Russell Westerholm, UniversityHerald Reporter

A study using sightings from a NASA telescope may have answered an old mystery surrounding centaurs, according to a NASA Jet Propulsion Laboratory (JPL) news release.

Centaurs are small stellar bodies orbiting the sun between Jupiter and Neptune and scientists have not been able to determine if they are comets or asteroids. A study based on images from NASA's Wide-field Infrared Survey Explorer (WISE) suggests they are comets.

Centaurs get their name from the creature of Greek mythology with a human's torso and horse's legs. The galactic mystery was named "centaur" because it shared characteristics of both an asteroid and a comet.

"Just like the mythical creatures, the centaur objects seem to have a double life," said lead author James Bauer of NASA's JPL in Pasadena, Calif. "Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system." 

"Cometary origin" means the centaur is made of the same material as a comet and may be inactive for now and could be active in the future. The study, published online July 22 in the Astrophysical Journal, analyzed infrared images of 52 centaurs in the sky, 15 of which were new discoveries.

Centaurs and their distant cousin, scattered disks, are part of an unstable belt orbiting the sun between Jupiter and Neptune. The two massive planets' gravitational force either pulls the centaurs and disks away from their locations or toward the sun.

Astronomers in the past have observed some centaurs and seen dark halos around them, regularly associated with outgassed comets. NEOWISE, WISE's asteroid-spotting component, can tell whether the centaur has a matte dark surface or a shiny reflective one.

Combined with what was already known about comet and asteroid colors, NEOWISE helped the scientists piece together the rest. Objects with a blue-gray color were more likely to be comets, while red objects were more likely asteroids.

Results showed that about two-thirds of the population of centaurs was comets.

"Comets have a dark, soot-like coating on their icy surfaces, making them darker than most asteroids," said the study's co-author, Tommy Grav of the Planetary Science Institute in Tucson, Ariz. "Comet surfaces tend to be more like charcoal, while asteroids are usually shinier like the moon."

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