Up to 60% of the objects nearest Earth could be “dark comets.”

PhysOrg reports on mysterious chunks of hard-to-see space rock all around us, even now. They contained – and might still contain – ice, which University of Michigan astronomers say means that they could one day be used to transport water around the solar system:

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

The study also shows a potential pathway for delivering ice into the near-Earth solar system, according to Taylor. How Earth got its water is a longstanding question.

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

Dark comets are a bit of a mystery because they combine characteristics of both asteroids and comets. Asteroids are rocky bodies with no ice that orbit closer to the sun, typically within what’s 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 into gas.

The study examined seven dark comets and estimates that between 0.5 and 60% of all near-Earth objects could be dark comets, which do not have comae but do have nongravitational accelerations. The researchers also suggest that these dark comets likely come from the asteroid belt, and because these dark comets have nongravitational accelerations, the study findings suggest asteroids in the asteroid belt contain ice.

“We think these objects came from the inner and/or outer main asteroid belt, and the implication of that is that this is another mechanism for getting some 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 objects like this out there. This could be a significant fraction of the nearest population. We don’t really know, but we have many more questions because of these findings.”


You can read more of Taylor’s findings here, in Icarus.