Space centaurs are small celestial bodies revolving around the sun and its real identity, whether be it an asteroid or comet, is one of the long term mysteries of astrophysics.

Until now, astronomers are unsure if centaurs are asteroids that tossed out from the inner solar system or comets traveling in toward the sun. But a new study of observations from NASA’s Wide-field Infrared Survey Explorer (WISE) finds that most centaurs are comets.

"Just like the mythical creatures, the centaur objects seem to have a double life. Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system," said James Bauer of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Bauer is lead author of a paper published online July 22 in the Astrophysical Journal.

NEOWISE, the asteroid-hunting part of the WISE mission, collected 52 infrared photos of centaurs and their more distant cousins, called scattered disk objects. Fifteen of which are new discoveries. Centaurs and scattered disk objects revolve in an unsteady belt and in time, gravity from the giant planets will toss them either closer or farther to the sun.

Astronomers had not been able to guesstimate the numbers of comets and asteroids even if they have formerly found evidence for comets in group and some centaurs with dusty halos, a distinguishing feature of an out gassing comet.

NEOWISE have provided information, through infrared, about the objects’ reflectivity or albedos, for astronomers to be able to sort population. Everything fell into place when astronomers combined the albedo information with the colors of the objects that are known. Centaurs, based on visible-light observations are either blue-gray or reddish in hue. NEOWISE showed that blue-gray objects comets and reddish objects are more likely to be an asteroid.

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

The outcome pointed out that approximately two-thirds of the centaur population is comets, which come from the frigid outer reaches of our solar system. However, it is not clear whether the remaining are asteroids. The centaur bodies are still mysterious, but future research from NEOWISE may reveal their secrets further.