The first dark comet—a celestial object that looks like an asteroid but moves through space like a comet—was reported less than two years ago. Soon after, another six were found. In a new paper, researchers announce the discovery of seven more, doubling the number of known dark comets, and find that they fall into two distinct populations: larger ones that reside in the outer solar system and smaller ones in the inner solar system, with various other traits that set them apart.
The first dark comet—a celestial object that looks like an asteroid but moves through space like a comet—was reported less than two years ago. Soon after, another six were found. In a new paper, researchers announce the discovery of seven more, doubling the number of known dark comets, and find that they fall into two distinct populations: larger ones that reside in the outer solar system and smaller ones in the inner solar system, with various other traits that set them apart.
The findings were published on Monday, Dec. 9, in the Proceedings of the National Academy of Sciences.
Scientists got their first inkling that dark comets exist when they noted in a March 2016 study that the trajectory of «asteroid» 2003 RM had moved ever so slightly from its expected orbit. That deviation couldn’t be explained by the typical accelerations of asteroids, like the small acceleration known as the Yarkovsky effect.
«When you see that kind of perturbation on a celestial object, it usually means it’s a comet, with volatile material outgassing from its surface giving it a little thrust», said study co-author Davide Farnocchia of NASA’s Jet Propulsion Laboratory in Southern California.
