Astronomers estimate that up to 60% of near-Earth objects could be dark comets

According to a University of Michigan study, up to 60% of near-Earth objects could be dark comets, mysterious asteroids orbiting the Sun in our solar system that likely contain or once contained ice and could be one of the routes for delivering water to Earth. .

The findings suggest that asteroids in the asteroid belt, the region of the solar system roughly between Jupiter and Mars that contains much of the system’s rocky asteroids, have subsurface ice, something that had been suspected since the 1980s, according to Aster Taylor , UM. graduate student in astronomy and lead author of the study.

The study also shows a potential route for the supply of ice to the near-Earth solar system, according to Taylor. How the Earth got its water is a long-standing question.

“We don’t know if these dark comets delivered water to Earth. We can’t say that. But what we can say is that there’s still debate about exactly how Earth’s water got here,” Taylor said. “The work we’ve done has shown that this is another way to get ice from somewhere in the rest of the solar system into Earth’s environment.”

The research further suggests that one large object may come from comets of the Jupiter family, comets whose orbits take them close to the planet Jupiter. The results of the team are published in the journal Icarus.

Dark comets are a bit of a mystery because they combine the properties of both asteroids and comets. Asteroids are rocky bodies without ice that orbit closer to the Sun, usually within what is called the ice line. This means they are close enough to the Sun for any ice the asteroid may have been carrying to sublimate, or change from solid ice directly to gas.

Comets are icy bodies that exhibit a fuzzy coma, a cloud that often surrounds a comet. Subliming ice carries dust with it and creates a cloud. Additionally, comets typically have modest accelerations driven not by gravity but by sublimation of ice, called non-gravitational acceleration.

The study examined seven dark comets and estimates that between 0.5% and 60% of all near-Earth objects could be dark comets that do not have a coma but have non-gravitational acceleration. The researchers also suggest that these dark comets probably come from the asteroid belt, and since these dark comets have non-gravitational acceleration, the results of the study suggest that the asteroids in the asteroid belt contain ice.

“We think these objects come from the inner and/or outer main belt asteroids, and the implication is that this is another mechanism for getting ice into the inner solar system,” Taylor said. “There may be more ice in the inner main belt than we thought. There may be more such objects outside. It may be a significant fraction of the nearest population. We really don’t know, but we have a lot more questions because of these findings.”

In previous work, a team of researchers including Taylor identified non-gravitational acceleration on a set of near-Earth objects and named them “dark comets.” They found that the non-gravitational acceleration of dark comets is likely the result of small amounts of sublimating ice.

In the current work, Taylor and their colleagues wanted to find out where the dark comets came from.

“Near-Earth objects don’t stay in their current orbits very long because the near-Earth environment is chaotic,” they said. “They only stay in the near-Earth environment for about 10 million years. Since the solar system is much older, that means that the near-Earth objects come from somewhere—that we’re constantly being fed near-Earth objects from another, much larger source.”

To determine the origin of this population of dark comets, Taylor and coauthors created dynamical models that assigned non-gravitational accelerations to objects from different populations. They then modeled the path these objects would follow with a given non-gravitational acceleration over a period of 100,000 years.

Scientists observed that many of these objects ended up where dark comets are today, and found that of all the potential sources, the main asteroid belt is the most likely place of origin.

One of the dark comets, called 2003 RM, which passes through an elliptical path close to Earth, then out to Jupiter and back around Earth, follows the same path we would expect from a comet in the Jupiter family, Taylor says — that is, its position. is consistent with a comet being knocked inward from its orbit.

Meanwhile, the study found that the rest of the dark comets probably came from the inner belt of the asteroid belt. Since dark comets are likely to contain ice, this indicates that ice is present in the inner main belt.

The researchers then applied the previously proposed theory to their population of dark comets to determine why the objects are so small and rapidly rotating. Comets are rocky structures held together by ice — think of a dirty ice cube, Taylor says. Once it hits the solar system’s ice line, the ice begins to release gas. This causes the object to accelerate, but it can also cause the object to spin quite quickly – fast enough to break the object apart.

“There will also be ice on those pieces, so they will also spin faster and faster until they break into more pieces,” Taylor said. “You can keep doing this as you get smaller and smaller and smaller. We suggest that you get these small, fast-spinning objects by taking several larger objects and smashing them into pieces.”

As this happens, the objects continue to lose their ice, becoming even smaller and rotating even faster.

The researchers believe that while the larger dark comet, 2003 RM, was likely a larger object that was ejected from the outer main belt of the asteroid belt, the six other objects they examined likely came from the inner main belt and were produced by an object that collided in and then he broke down.