Chaos In Solar System Explained

Solar system planets: Mercury, Venus, Mars, Earth, Jupiter, Saturn, Neptune, Uranus and Pluto. AP

By using a computer to play a complex game of "what if," scientists have developed a tale of chaos in the early solar system that they say explains several mysteries about why our cosmic neighborhood turned out the way it did.

"We get so many of the answers right," said Harold Levison of the Southwest Research Institute in Boulder, Colo. "I never dreamed it would be so spectacularly successful."

In a single stroke, he and his colleagues say, the tale answers such questions as:

What set off an intense asteroid bombardment some 3.9 billion years ago that created huge lava-filled basins on the moon and may have set back the development of life on Earth?

Why did Jupiter and Saturn leave their circular orbits and take on the more oval paths seen today? And how did their orbits become so tilted compared to other planets?

Why does Jupiter share its orbit around the sun with a swarm of asteroids?

The work is presented in Thursday's issue of the journal Nature by Alessandro Morbidelli of the Cote d'Azur Observatory in Nice, France, along with Levison and others. They used computer simulations to study various scenarios about how the outer solar system may have developed.

Their favorite scenario follows the generally accepted idea that the sun and planets formed from the gravitational collapse of a cloud of gas, dust and ice some 4.6 billion years ago. But it adopts what Levison called the controversial position that the solar system started out as quite compact. In this scenario, for example, Neptune starts out less than 15 times as far away from the sun as Earth is now, rather than the 23 times other scientists propose.

So the question was what would happen over eons as the planets followed circular orbits, surrounded by a huge ring of planetary rubble, chunks measuring up to hundreds of miles across. As the planets and chunks of rubble exerted their gravitational tugs on each other, what would change?

Here's what the scenario suggests:

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