Washington: A new study of observations from NASA`s Wide-field Infrared Survey Explorer (WISE) has revealed that most centaurs - the small celestial bodies orbiting the sun between Jupiter and Neptune - are actually comets.
Until now, astronomers were not certain whether centaurs are asteroids flung out from the inner solar system or comets travelling in towards the sun from afar.
Because of their dual nature, they take their name from the creature in Greek mythology whose head and torso are human and legs are those of a horse.
"Just like the mythical creatures, the centaur objects seem to have a double life," lead author James Bauer of NASA`s Jet Propulsion Laboratory (JPL) in Pasadena, California, said.
"Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system," he said.
Cometary origin means an object likely is made from the same material as a comet, may have been an active comet in the past, and may be active again in the future.
The findings come from the largest infrared survey to date of centaurs and their more distant cousins, called scattered disk objects.
NEOWISE, the asteroid-hunting portion of the WISE mission, gathered infrared images of 52 centaurs and scattered disk objects. Fifteen of the 52 are new discoveries.
Centaurs and scattered disk objects orbit in an unstable belt. Ultimately, gravity from the giant planets will fling them either closer to the sun or farther away from their current locations.
The study is published online in the Astrophysical Journal.