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NASA researchers have announced the discovery of seven additional dark comets, celestial bodies that appear asteroid-like but exhibit cometary behavior. This finding doubles the total known count to 14 and reveals two distinct populations based on size, location, and orbital characteristics within the solar system. 
by Clarence Oxford
Los Angeles CA (SPX) Dec 10, 2024
NASA researchers have announced the discovery of seven additional dark comets, celestial bodies that appear asteroid-like but exhibit cometary behavior. This finding doubles the total known count to 14 and reveals two distinct populations based on size, location, and orbital characteristics within the solar system. The new results were published on Dec. 9 in the *Proceedings of the National Academy of Sciences*.
The concept of dark comets emerged after the 2016 study of "asteroid" 2003 RM, whose unexpected orbital deviation could not be explained by known asteroid dynamics, such 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 Davide Farnocchia, a coauthor of the study and a researcher at NASA's Jet Propulsion Laboratory (JPL). Despite the telltale signs of outgassing, 2003 RM lacked any visible cometary tail.
The following year, a breakthrough occurred with the discovery of 'Oumuamua, the first interstellar object observed traversing our solar system. Its behavior mirrored that of 2003 RM, further intensifying interest in these peculiar celestial objects. "The fact that the first object we discovered from interstellar space exhibited similar behaviors to 2003 RM made 2003 RM even more intriguing," Farnocchia explained.
By 2023, scientists had classified seven solar system objects under the category of dark comets. This year's discovery of seven more dark comets enabled researchers to identify two primary subtypes. "We had a big enough number of dark comets that we could begin asking if there was anything that would differentiate them," said Darryl Seligman, lead author of the study and a postdoctoral fellow at Michigan State University. "By analyzing the reflectivity, or albedo, and the orbits, we found that our solar system contains two different types of dark comets."
Two Dark Comet Types
The research identifies outer dark comets, which share traits with Jupiter-family comets, including highly elliptical orbits and sizes exceeding hundreds of meters. In contrast, inner dark comets are smaller, typically tens of meters or less, and follow nearly circular orbits in the inner solar system, near Mercury, Venus, Earth, and Mars.These discoveries have spurred new questions about dark comets' origins and properties. Researchers are keen to understand their anomalous acceleration and whether they harbor ice. "Dark comets are a new potential source for having delivered the materials to Earth that were necessary for the development of life," said Seligman. "The more we can learn about them, the better we can understand their role in our planet's origin."
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