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NASA: Space centaurs are likely comets

Centaurs, small solar system bodies that orbit the sun between Jupiter and Neptune, have long been considered one of the more mysterious cosmic bodies in observable space. Astronomers questioned whether or not the bright objects are asteroids or comets, but a new study released online with the Astrophysical Journal supposes that it finally has the answer.

The name “centaur” was given to the objects due to the duality of their comet/asteroid characteristics, not unlike the dual horse/man dichotomy of the mythical beast. That’s where the similarities stop, however, and even the basic duality of cosmic centaurs may no longer hold applicable now that data from NASA’s Wide-field Infrared Survey Explorer, or WISE, has gathered strong evidence that they are in fact comets.

“Just like the mythical creatures, the centaur objects seem to have a double life,” said James Bauer in a statement from NASA’s Jet Propulsion Laboratory. “Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system.”

Bauer is the lead author of the new study on centaurs, which appeared online on July 22. The phrase “cometary origin” addresses the fact that centaurs might have been active comets in the past or could be active again in the future. These qualities are partly how comets are differentiated from asteroids, which originate from the inner solar system.

The new data from WISE highlights further differences between comets and asteroids and favors centaurs as examples of the former. NEOWISE, the segment of the WISE program dedicated to locating asteroids, performed the largest infrared survey of centaurs and a number of scattered disk objects. It located 52 objects in all, 15 of which are new discoveries.

A study of the bodies’ albedos, or the ratio of light reflected by a cosmic object to that received by it, compared new information of the centaurs’ color to what has been collected in the past. Visible-light data has pegged centaurs as either blue/gray in color or having a red hue. While blue/gray objects can be either comets or asteroids, dark blue/gray objects are typically comets. Reddish objects are usually considered to be asteroids.

Tommy Grav, researcher with the Planetary Science Institute in Tucson, AZ, and co-author of the study, said that comets have surfaces like charcoal and that asteroids are shiny, much like the moon. Two-thirds of the centaurs observed had coloration that was indicative of a comet. It remains unclear if the final third is made up of comets or asteroids.

“That means the small body populations found beyond the Main Asteroid Belt, like the Hildas, Jupiter Trojans and Centaurs, were either formed where they currently are, or they were inbound objects coming from the far reaches of the Solar System that settled into their current orbits,” said Grav in a press release.

For now, NEOWISE will continue to study the centaurs for more information.