Was a giant planet kicked out?

Computer simulations suggest that a giant planet was kicked out of our solar system billions of years ago, saving Earth in the process. But how solid are those simulations?

The concept appears in a paper written by David Nesvorny, a researcher at the Southwest Research Institute, and published in The Astrophysical Journal Letters. His findings aren't based on the discovery of an actual Planet X, but instead are the result of thousands of simulations re-enacting the dynamical development of our planetary system.

Past simulations have shown that the solar system's current configuration is the result of a complex dance of the planets: About 600 million years into the solar system's existence, gravitational interactions caused a series of orbital shifts and scatterings. Astronomers believe that Jupiter moved inward and scattered many of the solar system's smaller bodies outward. Meanwhile, Saturn, Uranus and Neptune moved outward. Some models even suggest Uranus and Neptune switched places as they moved out.

This scenario explains phenomena ranging from the distribution of small bodies on the solar system's edge to the cratering rate on the moon. However, Jupiter's behavior in the model had to be tweaked: If Jupiter's orbit moved inward gradually, the giant planet would have stirred up the inner solar system too much. Earth's orbit could have been disrupted so much that it would have crashed into Mars or Venus.

"Colleagues suggested a clever way around this problem," Nesvorny said in a news release issued this week by the Southwest Research Institute. "They proposed that Jupiter's orbit quickly changed when Jupiter scattered off of Uranus or Neptune during the dynamical instability in the outer solar system."

This maneuver, known as the jumping-Jupiter hypothesis, would be less disruptive for the inner solar system. Nesvorny decided to test the idea by running billions of years' worth of simulations. He found Read more