Could asteroids, which are remnants of comets, be one of the main sources of water on Earth?
Up to 60% of near-Earth objects could be dark comets, mysterious asteroids orbiting the sun in our solar system that probably contain or once contained ice and may have been one of the pathways by which water reached Earth, according to a University of Michigan study.
The findings suggest that asteroids in the asteroid belt, a region of the solar system roughly between Jupiter and Mars where most of the rocky asteroids are found, have subsurface ice, as suspected since the 1980s, according to the study's lead author, Esther Taylor of the University of Michigan.
The study also shows a potential pathway for bringing ice into the solar system close to Earth, according to Taylor. The question of how the country obtained its water has been studied for a long time.
"We don't know if these dark comets brought water to Earth. We can't say that. But we can say that there is still some debate about exactly how Earth's water got here," Taylor said. "The research we did showed that this is another route for bringing water from somewhere in the rest of the solar system to the vicinity of the country."
The study also suggests that one large object may come from Jupiter family comets, comets whose orbits take them close to the planet Jupiter. The results of the study are published in the journal Icarus.
Dark comets are somewhat mysterious because they combine characteristics of asteroids and comets. Asteroids are rocky bodies without ice that orbit closer to the Sun, usually within the so-called ice line. This means that they are close enough to the Sun for ice that might be in the asteroid to lift off, i.e. turn from solid ice directly to gas.
Comets are icy bodies that show a hazy halo (floor), a cloud that often surrounds a comet. The rising ice carries dust with it, which forms the cloud. In addition, comets usually have a slight acceleration whose origin is not gravity but the ice mirror, known as non-gravitational acceleration.
In the study, they examined seven dark comets and estimated that between fifty and sixty percent of all near-Earth objects could be dark comets, which do not have a halo but have non-gravitational acceleration. According to the researchers, these dark stars probably come from the asteroid belt, and because they have non-gravitational acceleration, the research findings indicate that asteroids in the asteroid belt contain ice.
"We think these objects come from the inner and/or outer main asteroid belt, and the implications are that this is another mechanism for bringing ice into the inner solar system," Taylor said. There may be more ice in the inner main belt than we thought. There could be more such objects somewhere. This can be a significant fraction of the population of closest objects. We don't really know, but we have many more questions because of these findings."
In the current study, the researchers wanted to find out where the dark comets come from. "Near-Earth objects do not stay in their current orbits for long, only around 10 million years, because the environment close to Earth is messy," they said. "The solar system is much older, so the meaning is that they come from somewhere - we constantly receive near-Earth objects from another, much larger source."
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