Scientists have discovered seven more “dark comets” and analysis of the batch shows the puzzling asteroids are split into two distinct families, further deepening the mystery of why these objects look like asteroids but behave like The mystery of the comet.
Recently, the dividing line between asteroid and comet It has become blurry. have”main belt comet“Also known as active asteroids, they are comet-like objects that have the properties of asteroids. And then there are dark comets, which are the opposite: asteroids that have some of the properties of comets.
As the name suggests, main-belt comets tend to inhabit main-belt comets. asteroid belt between Mars and Jupiter. But they have tails like comets, whereas dark comets don’t have tails but move like comets, in the sense that they exhibit non-gravitational acceleration. In other words, in addition to gravity, there are some other forces acting on their motion, changing their trajectories. For ordinary comets, another force is the push caused by ice sublimating into vapor on its surface as it approaches the comet’s heat. sun The gas is then released into space, carrying with it the dust that creates the signature tail. However, dark comets have no tails.
“When you see this kind of disturbance on an object, it usually means it’s a comet,” Davide Farnocchia of NASA’s Jet Propulsion Laboratory in Southern California said in a report. Volatiles released from its surface give it a little push. statement. “But despite our best efforts, we couldn’t find any sign of the comet’s tail.”
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We’ve seen this mysterious move before. 2017, interstellar objects 1I/’Oumuamua Quickly travel through the heart solar system Then return to interstellar space. As it did so, its trajectory changed from the one planned for it by gravity alone—”Oumuamua seemed to be getting an extra push from somewhere.”
Although no tail or outgassing from ‘Oumuamua has been detected, leading to its lingering mystery, ‘Oumuamua’s behavior is very similar to another unusually behaving object discovered a year ago.
The object, known as 2003 RM, was thought to be just another asteroid until it was also discovered to be moving without gravity.
“The fact that the first object we discovered from interstellar space exhibits similar behavior to 2003 RM makes 2003 RM even more interesting,” Farnocchia said.
By 2023, six more similar objects were discovered, and the term “dark comet” was used for the first time because these objects behave like comets but don’t emit the light that comets do – although they are still visible as through powerful The light spot of the telescope is the same. It is assumed that dark comets are outgassing, but only to an almost imperceptible extent, just enough to provide them with propulsion.
Now, seven more dark comets have been discovered, bringing the total to 14 — enough to start drawing some conclusions about their properties.
“We have enough dark comets that we can start asking if there is anything that distinguishes them,” said Darryl Seligman of Michigan State University, who led the new study. “By analyzing reflectance [of the surface of the dark comets, which is related to their composition] and orbits, we found that our solar system contains two different types of dark comets.
One of the realms lurking in the outer solar system gas and ice giants. Another group is located in the inner solar system, with mercury, Venus, Earth and Mars. The outer dark comets are larger, hundreds of meters or more in diameter, while the inner dark comets are much smaller, tens of meters or less in diameter.
The outer dark comets have more quirks, with elliptical orbits more like the orbits of typical comets, while the inner dark comets have orbits more like the circular orbits of planets. Seligman pointed out that outer dark comets have some characteristics similar to Jupiter family cometsthese comets wander from the outermost reaches of the solar system and settle in orbits around the sun that extend no farther than Jupiter.
However, the why and wherefore remains a mystery. How did dark comets appear in these two places? In the summer of 2024, Seligman’s team show If inner dark comets are perturbed by birth zones in the inner region of the asteroid belt, they may at least stay in their current orbits.
Related: ‘Dark comets’ may have provided Earth with water long ago
There’s also the question of how much water ice dark comets contain. When the solar system was formed 4.5 billion years ago, there was an invisible dividing line called “snow line” Inside the snow line, which is a little closer to the sun than Jupiter’s current position (about 5 astronomical unit — About 465 million miles (or 750 million kilometers) away, temperatures in the protoplanetary disk were too hot for ice to form, and water existed as vapor or liquid. Beyond the snow line, where the outer solar system planets now reside, temperatures were cold enough that water could freeze into ice.
Therefore, it would not be surprising if the outer layers of dark comets contain ice beneath their surfaces. But inner dark comets that appear to form inside the snowline must also contain ice so that they can expel gas and generate non-gravity-accelerating thrust. Early work by Seligman’s team showed up to 60% of near earth object Possibly a dark comet, raising the possibility of a dark comet that struck Earth long ago Bring water to our planet.
“Dark comets are a new potential source of delivering materials needed for the development of life to Earth,” Seligman said. “The more we learn about them, the better we can understand their role in the origin of our planet.”
Discovery of seven new dark comets Reported on December 9 In the journal Proceedings of the National Academy of Sciences.