In 2016, astronomers were puzzled when asteroid 2003 RM veered slightly off its expected course.
The strange event sparked curiosity, as the object looked like an asteroid but acted more like a comet. By 2023, seven similar objects were identified, all defying traditional definitions.
These hybrids were dubbed "dark comets."
Now they have been studied in greater detail, and the results could reshape our understanding of the solar system.
Researchers from NASA's Jet Propulsion Laboratory and Michigan State University have analyzed 14 of these enigmatic objects and uncovered startling complexity.
Their findings, published in the Proceedings of the National Academy of Sciences, categorize dark comets into two distinct groups, challenging long-standing definitions of comets and asteroids.
What Makes Dark Comets So Unique?
Traditionally, comets are icy bodies that release gas and dust as they approach the Sun, creating the iconic tail. Asteroids, on the other hand, are rocky or metallic and don’t emit gas.
But dark comets combine traits of both.
Like comets, their orbits can change due to gas emissions when exposed to the Sun.
Unlike traditional comets, they lack visible tails.
They also don’t display the Yarkovsky effect, a phenomenon where an asteroid's orbit changes due to uneven heating and cooling caused by solar radiation.
The research categorized dark comets into two groups based on their orbits and sizes:
Outer Dark Comets:
These objects originate from the Kuiper Belt and have elliptical orbits. They are larger, measuring hundreds of meters or more in diameter.Inner Dark Comets:
Found in the inner solar system, these are smaller, with diameters of less than 10 meters. They move in nearly circular orbits.
Why Do They Matter?
Dark comets may provide new clues about the early solar system.
Unlike asteroids or traditional comets, they could serve as a previously unrecognized source of organic materials and water, potentially aiding the development of life on Earth.
"Dark comets are a new potential source for delivering the materials to Earth that were necessary for the development of life," said Darryl Seligman of Michigan State University in a press release. "The more we can learn about them, the better we can understand their role in the origins of our planet."
