NASA has revealed the discovery of seven new “dark comets,” bringing the total of this strange new class of objects to 14.
Dark comets are a newly defined type of near-Earth object somewhere between an asteroid and a comet. Described by planetary scientists as comets and asteroids whose orbits of the sun bring them close to Earth, they resemble asteroids but tend to speed up unexpectedly, suggesting they may be firing jets of gas, as comets do.
However, they have no coma around their nucleus. They’re also dark — making them akin to 1I/’Oumuamua, the interstellar object spotted in 2017 that was passing through the solar system.
Dark Comets: The Two Populations In The Solar System
Published yesterday in the Proceedings of the National Academy of Sciences, a new paper reports the detections of seven dark comets in two distinct populations. They posit that larger dark comets reside in the outer solar system while smaller dark comets exist in the inner solar system.
“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 and a postdoctoral fellow in the Department of Physics at Michigan State University, East Lansing. “By analyzing the reflectivity,” or albedo, “and the orbits, we found that our solar system contains two different types of dark comets.”
Dark Comets: More Common Than Anyone Thought
The authors suggest that dark comets, such as volatiles and organics, may have delivered material to the Earth necessary for the development of life. That’s exactly what was suggested by a paper published in July in Icarus, which argued that dark comets are much more common than previously thought and may have delivered water to Earth long ago.
That study examined seven dark comets but estimated that between 0.5 and 60% of all near-Earth objects could be dark comets from the asteroid belt between Mars and Jupiter. Since dark comets contain ice — as comets do, but asteroids do not — they could be the mechanism by which water enters the inner solar system.
Dark Comets: The Asteroid that Wanted to be a Comet
The first dark comet was found in 2016 when scientists described the trajectory of an asteroid called 2003 RM, which appeared to move slightly from its orbit in a way thought only possible by comets propelled by jets of gas.
“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, coauthor from NASA’s Jet Propulsion Laboratory, California. “But try as we might, we couldn’t find any signs of a comet’s tail. It looked like any other asteroid — just a pinpoint of light. So, for a short while, we had this one weird celestial object that we couldn’t fully figure out.”
That discovery of “The Asteroid that Wanted to be a Comet” was followed a year later by the discovery of 1I/’Oumuamua, the interstellar object that also appeared as a single point of light, like an asteroid, but had a trajectory like a comet. “The fact that the first object we discovered from interstellar space exhibited similar behaviors to 2003 RM made 2003 RM even more intriguing,” said Farnocchia.
Dark Comets: A New Potential Source Of Water — And Life?
If, how and when dark comets delivered water to Earth is going to be difficult to prove. The main asteroid belt is the most likely source of near-Earth objects, but such objects remain on their current orbits only for about 10 million years. The solar system is about 4.5 billion years old.
“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.”
Wishing you clear skies and wide eyes.
