The origin of the asteroid belt is closely linked to the history of our Solar System, and astronomers thought they had a good idea of how it formed. But a new study has come out today to contradict those ideas.
It is generally thought the belt came from the same source the rocky planets are made from, called planetesimals. Beyond Mars, the gravity from Jupiter was too strong for these rocks to form planets, so they stayed as smaller, rocky remains such as asteroids.
In this theory, the amount of mass in the asteroid belt dropped by 99 per cent in the Solar System’s first 100 million years. But exactly how it lost all this mass has, until now, been a bit of a mystery.
A new study shows this might not be the case. Instead, in the early Solar System, the asteroid belt started out empty and was later filled by the planets ‘kicking out’ debris, making it a kind of cosmic refugee camp.
The study claims C type asteroids, which contain carbon, were kicked out from the gas giants while S type asteroids, which contain silicates and are mainly found in the inner asteroid belt, came from the rocky planets.
“Models of Solar System formation had made the assumption that the asteroid belt once contained a large amount of material that was later depleted,” says Sean Raymond, from the University of Washington, lead author of the paper, published in the journal Science Advances. “To give you a scale, these models needed to remove about 99.9 per cent, but not 100 per cent, of the material that started off in the belt. Some models were successful, but this was a big challenge.”
But what if it started out as nothing?
“Our approach in this paper was to assume the exact opposite, that the belt started off empty and then needed filling later,” Raymond says. “The answer is that, starting from an empty belt, a belt that looks a lot like the current one is populated effortlessly. I didn’t expect it to work quite so easily, to be honest.”
Now this model has been shown to work, the next step will to be to work out who is right. “One step will be to try to address the differences between models to see if we can shoot any of them down,” Raymond explains. “At the same time, broadening our thinking to try to understand why the Solar System looks different than most extra-solar planetary systems.”