Space centaurs are a real phenomenon and researchers may have discovered what these small celestial objects are based on new observations. According to NASA, researchers have determined the majority of centaurs are comets.

Centaurs, not to be confused with the mythical half-horse, half-human creature, are small objects orbiting around the sun and can found between Jupiter and Neptune. These small bodies have been puzzling researchers trying to determine if they are asteroids or comets. There are two main differences between asteroids and comets, comets are usually further away from the sun with an irregular orbit. Asteroids have a more consistent orbit and are found much closer to the sun.  The chemical composition of the comet’s icy surface produces a coma, a temporary atmosphere, or a tail as it approaches the sun while an asteroid does not produce a coma or tail.

The small space bodies got their name as homage to the mythical creature. Researchers were unsure if they were displaced asteroids or comets heading towards the sun, notes NASA. Using the Wide-field Infrared Survey Explorer, WISE, researchers were able to observe the centaurs in better detail which led them to conclude the majority of bodies were comets. James Bauer, from NASA’s Jet Propulsion Laboratory, said of the celestial bodies, “Just like the mythical creatures, the centaur objects seem to have a double life.” The research was published in the Astrophysical Journal.

According to NASA, WISE scans the whole sky to observe extremely dark celestial objects. Part of WISE’s mission is to hunt for faint comets or asteroids and the researchers used this aspect of the mission, named NEOWISE, to discover the true identity of the centaurs.  NEOWISE was collecting on 52 centaur objects, 15 of which were new discoveries, and comets from even further out in space, called scattered disk objects. According to NASA, these objects are not as neatly organized in belts similar to the asteroid belt and their location may vary due to the gravitational pull from the nearby gas giants.  

NEOWISE was used to determine the reflectivity of the centaur objects and previous observations of these objects’ color led researchers to conclude the objects were comets. According to NASA, visible-light observations indicated a majority of the centaur objects were blue in color while some were redder in color. The reflectivity data collected NEOWISE determined the centaur objects were dark, indicating a low level of light being reflected from the surface.

According to the study’s co-author, Tommy Grav from the Planetary Science Institute in Arizona, comets have a dust covered surface which would not reflect a lot of light. Using the data collected by WISE and the previous observation of their color, researchers determined the majority of centaur objects were comets. “Comet surfaces tend to be more like charcoal, while asteroids are usually shinier like the moon,” said Grav.

The researchers did not conclude the remaining centaur objects, those that appeared redder in color, were asteroids and future research could determine the origins of the remaining centaur objects.