Jupiter may not be the "planetary shield" that many scientists make the gas giant out to be. Instead, new simulations suggest that Saturn may play a crucial role in steering asteroids away from Earth.

The "Jupiter as a shield" concept arose from a misinterpretation of a 1994 paper by George Wetherill - a planetary scientist at the Carnegie Institution who died in 2006 - says planetary scientist Kevin Grazier. Wetherill's paper argued that systems with "failed Jupiters" (that is, star systems only with planets of perhaps Uranus and Neptune's size or smaller) would have more densely populated cometary source regions, and that they "eject a smaller number of comets into interstellar space."

Grazier, of NASA's Jet Propulsion Laboratory who has also served as an advisor for "Battlestar: Galactica" and "Gravity," told Seeker that he tried to replicate Wetherill's work from 1994. The aim was to see what had changed with the more advanced computing power of today.

"You see [Jupiter's influence] recreated all the time in documentary TV shows," Grazier said. He reasoned that Saturn is a large planet, too. "I just thought about that [theory] and I said, 'I don't believe that for a moment.'"

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Grazier found that, through simulations, a typical small body - like an asteroid or comet - between Jupiter and Saturn will get kicked out, but many of them are ejected after they pass into the inner solar system. Further simulations (some dropping Jupiter from the equations, and some dropping Saturn) show that it takes both planets combined to reliably move objects out of the solar system. If only one planet of the two exists, a belt of material is created and only a few small bodies are removed from the solar system.