A long-standing hypothesis about Jupiter claims that the biggest planet in the solar system acts as a kind of shield for Earth, reducing the number of comets that make their way to Earth by capturing them with its massive gravitational pull. A 1994 scientific paper published in the journal Astrophysics and Space Science concluded that without Jupiter and Saturn, our solar system would have about 1,000 times more asteroids and comets orbiting its inner section — much to the detriment of life on Earth. Further, it was thought that having a planet of Jupiter’s size to shield a planet with Earth-like qualities might be a prerequisite for life to form elsewhere in the universe.

This "Jupiter as shield" theory is elegant, but new research conducted at NASA’s Jet Propulsion Laboratory (JPL) shows that it's probably incorrect — in fact, it may turn the concept upside-down, literally.

JPL’s Kevin Grazier, Ph.D., used computer models to simulate the evolution of 30,000 particles floating in the areas between the jovian planets of our solar system over periods of up to 100 million years. There are four Jupiter-like "gas giants": Jupiter, Saturn, Uranus and Neptune, with the biggest ones being the first two listed here.

Io, a moon of Jupiter, floating above the gas giant.Io, a moon of Jupiter, floating above the gas giant. (Photo: NASA/Cassini-Huygens)

These simulations showed that not only is Jupiter not a particularly effective protector, but it actually teams up with Saturn to throw particles down to the inner solar system where our planet lies. A significant number of these particles end up in orbits that cross Earth’s path.

It's theorized that some of these volatile materials from the outer regions of the solar system might have been beneficial for the emergence of life. Impacts that are very large can cause existential risk, like the Cretaceous-Paleogene extinction event when an asteroid 10 miles in diameter hit Mexico's Yucatán Peninsula, but smaller ones can act as a delivery mechanism for beneficial materials that might only have been present in low concentrations on the planet during earlier stages of its development.

It looks like Jupiter has been helping us after all, just not in the way we expected.

Michael Graham Richard ( @Michael_GR ) Michael writes for MNN and TreeHugger about science, space and technology and more.