Researchers have played out possible histories of the solar system on computers and come up with a chaotic game of cosmic billiards that helps explain several mysterious features of Earth’s neighbors.
“I never thought we would be able to do this, but it worked spectacularly well,” said Hal Levison of the Southwest Research Institute in Boulder. “Either we have one hell of a series of coincidences, or we’re on the right track.”
The detailed models, published in today’s issue of Nature, speak to at least three problems in planetary science: Why Jupiter and Saturn orbit the sun in ovals, not circles; how the moon became so deeply cratered; and why two small swarms of asteroids share Jupiter’s orbit.
The findings could help people understand how Earth became a habitable place and how the ingredients for life accumulated here, Levison said.
Levison and his colleagues – from Brazil, France and Greece – found they could reproduce today’s solar system if the following series of events happened about 4 billion years ago, when a disc of asteroid-like objects called planetesimals likely surrounded the solar system:
If the young solar system was fairly compact, some of those planetesimals could have leaked inward, bouncing like billiard balls among the planets.
Those interactions could have slowly pulled Jupiter inward and pushed Saturn, Uranus and Neptune outward.
When Jupiter fell into an orbit exactly twice as fast as Saturn’s, strange gravitational effects would have suddenly rearranged the outer planets, sending Jupiter and Saturn into elliptical orbits.
Neptune and Uranus would have plowed through the planetesimal disk, pushing some of the objects inward, where they would have smashed into Earth and the moon. Others would have been captured by Jupiter’s orbit.
“Our model explains so many things that we believe it must be basically correct,” said Alessandro Morbidelli, an astrophysicist with the Cote d’Azur Observatory in France.
In a commentary on the new reports, Canadian astrophysicist Joe Hahn wrote that scientists should be cautious about reading too much into the results.
A computer simulation that produces a realistic solar system is not proof that history happened that way, Hahn said. But the new theory deserves careful attention, he wrote, and it could well end up being a compelling explanation for the planets’ arrangements.
Staff writer Katy Human can be reached at 303-820-1910 or at khuman@denverpost.com.
