what are these enigmatic black comets observed by NASA?

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They are called “dark comets”, or “black comets”. And if their name sounds very science fiction, as if the big bad of a film resided there and used them for nefarious purposes, that is not the case.

In fact, scientists originally thought they were observing an asteroid, which seemed to behave like a comet. And then they found another, and then another. On December 9, 2024, NASA announced that seven new such specimens had been discovered, bringing the total to 14.

14 stellar objects, half-comet, half-asteroid, which have been called black comets, or dark comets.

An asteroid or a comet?

To put it simply, in March 2016, scientists realized that asteroid 2003 RM had “slightly deviated from the predicted orbit.” A gap that could not be explained.

“For a brief moment, we had this strange celestial object that we couldn't completely understand,” explains Davide Farnocchia, co-author of the study from NASA's Jet Propulsion Laboratory, on the NASA website. NASA in Southern California.

“When you see this kind of disturbance on a celestial object, it usually means that it is a comet, whose surface gives off volatile materials that give it a slight push. But despite our best efforts, we found no sign of a comet tail. It looked like any other asteroid, just a point of light. »

In other words, scientists thought they were observing an asteroid, composed mainly of rocks and metals, which therefore began to follow an unexpected trajectory. Due to potential outgassing. So, to the sublimation of volatile materials. Found on comets, but not on asteroids.

Except that behind it, they were never able to see a tail to this stellar object, like the one that accompanied the comet of the Tsuchinchan-ATLAS decade).

Hence this new name.

And what's more, there are two types

And now we have realized that there are actually two types of dark comets.

First the outer comets, which present “characteristics similar to those of the comets of the Jupiter family: they have very eccentric (or elliptical) orbits and are larger (hundreds of meters or more in diameter)”, note the scientists in Proceedings of the National Academy of Sciences.

And then, the “inner” comets, which reside in the inner solar system (Mercury, Venus, Earth, and Mars), travel in almost circular orbits and are rather small (a few tens of meters).

A “source of materials necessary for the development of life on Earth”?

However, we still do not know where they come from exactly, nor why they are accelerating like this. “Is it because they contain ice?” “, ask NASA scientists.

Either way, they present a “potential new source of materials necessary for the development of life on Earth,” enthused Darryl Seligman, a postdoctoral researcher in the physics department at Michigan State University, at East Lansing, and lead author of the new study. “The more we know about them, the better we will be able to understand their role in the origin of our planet. »

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