NASA researchers have made an intriguing discovery that could reshape our understanding of space and its hidden objects. A new class of celestial bodies—dubbed “dark comets”—has been identified, and researchers have recently doubled the number of known objects in this category. These dark comets behave like traditional comets, showing a unique interaction with their environment, but appear more like asteroids to the naked eye. Their peculiar characteristics and unusual trajectories have puzzled scientists since their first discovery less than two years ago.
In a new paper published in Proceedings of the National Academy of Sciences on December 9, 2024, researchers revealed the discovery of seven additional dark comets, bringing the total number to 14. This finding has not only expanded the catalog of known dark comets but also presented astronomers with a new set of questions.
What Are Dark Comets?
Dark comets are celestial objects that exhibit the characteristics of both comets and asteroids. They are objects that appear to be asteroids because they don’t have the typical tail that comets are known for. However, they share one crucial trait with comets: their trajectories are altered due to the outgassing of volatile material from their surface. This outgassing, which gives comets their famous tails, causes the objects to slightly change direction, an effect known as “non-gravitational acceleration.”
The first dark comet was detected in 2022, and this strange object—officially designated 2003 RM—showed peculiar deviations in its orbit. “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,” explained Davide Farnocchia, a scientist from NASA’s Jet Propulsion Laboratory, who worked on the study. However, the team couldn’t detect any traditional signs of a comet, like the expected tail of dust and gas. “So, for a short while, we had this one weird celestial object that we couldn’t fully figure out,” Farnocchia added.
The mystery deepened in 2017, when astronomers discovered ‘Oumuamua, the first interstellar object to pass through our solar system. Like 2003 RM, ‘Oumuamua showed strange acceleration as it moved through space. This discovery brought more attention to the concept of dark comets and led to the identification of several more in the years that followed.
Two Populations of Dark Comets
Thanks to a surge in discoveries, scientists have now classified dark comets into two main groups. The recent findings have shown that dark comets exist in two distinct populations: outer dark comets and inner dark comets.
- Outer Dark Comets: These larger comets, typically hundreds of meters across, orbit in highly eccentric, elliptical paths that stretch deep into the outer solar system. Their behavior is similar to that of Jupiter-family comets, which are often associated with large orbital distances and a high degree of orbital eccentricity.
- Inner Dark Comets: Unlike their larger counterparts, inner dark comets are smaller (usually tens of meters or less) and reside in the inner solar system. These objects travel in nearly circular orbits, similar to the orbits of planets like Earth, Venus, and Mars.
Darryl Seligman, a postdoctoral fellow at Michigan State University and the lead author of the study, explains the significance of these findings: “We had a big enough number of dark comets that we could begin asking if there was anything that would differentiate them. By analyzing the reflectivity, or albedo, and the orbits, we found that our solar system contains two different types of dark comets.”
This distinction opens up new questions about the origins of these objects and their relationship to other known space phenomena.
The Mystery of Dark Comets’ Origin
While the discovery of these two populations is a significant step forward, scientists are still left with several fundamental questions. The most pressing of these is where these dark comets come from. Are they remnants of the early solar system, left over from its formation billions of years ago? Or do they originate from outside the solar system, as their mysterious behaviors might suggest? “Dark comets are a new potential source for having delivered the materials to Earth that were necessary for the development of life,” Seligman said, hinting at a possible connection to the origins of life on Earth.
The study also raises questions about what these objects might contain. Do dark comets hold valuable materials like water or organic compounds? Could they help explain how life-sustaining molecules arrived on Earth?
As researchers continue to study these celestial bodies, they will undoubtedly uncover more answers. What is clear now is that dark comets represent a fascinating and mysterious aspect of our solar system that warrants further exploration.
