The first dark comet, a celestial body that looks like an asteroid but moves through space like a comet, was reported less than two years ago. Six more were soon found. In a new paper, researchers announced the discovery of seven more comets, doubling the number of known dark comets, and found that they are divided into two distinct populations: larger ones in the outer Solar System and smaller ones in the inner Solar System, along with a variety of others. features that distinguish them.

The results were published on December 9. Proceedings of the National Academy of Sciences.

Scientists first predicted the existence of dark comets in a March 2016 study when they noticed that the orbit of “asteroid” 2003 RM deviated slightly from the expected orbit. This deviation cannot be explained by typical asteroid accelerations, such as the small acceleration known as the Yarkovsky effect.

“When you see this kind of perturbation in a celestial object, it usually means it’s a comet; volatile material coming off its surface is pushing it a little bit,” said study co-author David Farnocchia of NASA’s Jet Propulsion Laboratory in Southern California. . “But no matter how hard we tried, we could not find any trace of the comet’s tail. It looked like any other asteroid; just a point of light. “So we briefly experienced a strange celestial object and couldn’t help but completely understand it.”

strange celestial objects

Farnocchia and the astronomy community didn’t have to wait long to get another piece of the puzzle. The following year, in 2017, a NASA-sponsored telescope discovered the first celestial object documented to have originated outside our solar system. 1I/2017 U1 (‘Oumuamua) not only appeared as a single point of light like an asteroid, its orbit also changed so that it appeared to eject volatile material from its surface like a comet.

“‘Oumuamua surprised us in many ways,” Farnocchia said. “The fact that the first object we detected in interstellar space exhibited similar behavior to 2003 RM made 2003 RM even more interesting.”

By 2023, researchers had detected seven objects in the Solar System that resemble asteroids but behave like comets. This was enough for the astronomy community to give them their own category of celestial bodies: “dark comets.” Now that researchers have found seven more such objects, they can begin a new set of questions.

“We had enough dark comets that we could start asking whether there was something that could distinguish them,” said Darryl Seligman, a postdoctoral researcher in the Department of Physics at Michigan State University in East Lansing and lead author of the study. new paper. “By analyzing the reflectance, or albedo, and orbits, we found that our solar system contains two different types of dark comets.”

Two types of dark comets

The study’s authors found that a type they call outer dark comets has similar characteristics to Jupiter family comets: They have highly eccentric (or elliptical) orbits and are on the larger side (hundreds of meters or more wide).

The second group, inner dark comets, are found in the interior of the Solar System (which includes Mercury, Venus, Earth, and Mars), move in nearly circular orbits, and are on the smaller side (tens of meters or less). ).

Like many other astronomical discoveries, Seligman and Farnocchia’s research not only expands our knowledge of dark comets, but also raises several additional questions: Where did dark comets come from? What causes their abnormal acceleration? Can they contain ice?

“Dark comets are a new potential source for delivering to Earth the materials necessary for the development of life,” Seligman said. he said. “The more we learn about them, the better we can understand their role in the formation of our planet.”