The solar system’s main asteroid belt may have taken its shape when three gas giant planets were flung into more distant orbits, scattering the remote, icy objects that were lurking at the solar system’s edge. A new study, published in Nature, suggests that the event sent “space invaders” to the belt between Mars and Jupiter that seem more like primitive frozen comets than the baked rocks that make up the overwhelming majority of asteroids [AP].
The findings support a recent theory for the solar system’s formation called the Nice model (named after the city in France), which suggests that all four gas giants originally formed near to the sun, but migrated in what “we believe was a very violent event that happened roughly 700 million years after the solar system formed,” when the solar system was in “its teenage years,” [SPACE.com], explains study coauthor Harold Levison. He says the original orbits of the gas giants weren’t stable, and “the orbits really just went kablooy”. Jupiter moved inwards, while Saturn, Uranus and Neptune all moved away from the Solar System’s centre. As they did so, they catapulted icy bodies from the early protoplanetary disc into the inner Solar System [Nature News].
While the Nice model hasn’t won universal acceptance yet, many researchers believe it solves the problems associated with the previous theory (which assumed that the planets formed in their present orbits but couldn’t explain how Uranus and Neptune could have formed at such a distance from the sun). The current study modeled how the movements of the gas giants would have impacted the icy objects at the edge of the solar system and found that some would have been flung back towards the center. Researchers say this asteroid reshuffling shown in the Nice model also explains other oddities in the solar system: the far-out Kuiper belt beyond Neptune; the so-called Trojan asteroids of Jupiter; and the Late Heavy Bombardment of the moon billions of years ago. “It really is the only model we have that can explain the solar system like we see [it]” [SPACE.com], says Levison.
Levison believes that, if this model is correct, detailed studies of the asteroid belt will tell astronomers more about how the early Solar System evolved. “It’s sort of like a crime scene investigation,” he says. “How the blood is splattered on the wall tells you more about what happened than the body itself” [Nature News].
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Image: NASA / JPL-Caltech