New observations from NASA's NEOWISE project reveal the hidden nature of centaurs, objects in our solar system that have confounded astronomers for resembling both asteroids and comets. The centaurs, which orbit between Jupiter and Neptune, were named after the mythical half-horse, half-human creatures called centaurs due to their dual nature. This artist's concept shows a centaur creature together with asteroids on the left and comets at right.

The results suggest that roughly two-thirds of the centaur population have cometary origins, hailing from the frigid outer reaches of our solar system. It is not clear if the remaining one-third of the population is made up of asteroids.

NEOWISE, the asteroid-hunting portion of NASA's Wide-field Infrared Survey Explorer, was able to crack the centaur mystery thanks to its ability to see the infrared properties of the small objects. The infrared data, together with previous visible-light observations, showed that many of the centaurs are dark like soot and blue-gray in color, telltale signs of comets.

Image credit: NASA/JPL-Caltech

› Related release