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Wandering Jupiter could have swept inner solar system clean

By sciencenews.org

A wandering baby Jupiter could help explain why there are no planets closer to the sun than Mercury and why the innermost planet is so tiny, a new study suggests.

Jupiter’s core might have formed close to the sun and then meandered through the rocky planet construction zone. As the infant Jupiter moved, it would have absorbed some planet-building material while kicking out the rest. This would have starved the inner planets — Mercury, Venus, Earth and Mars — of raw materials, keeping them small and preventing any other planets from forming close to the sun, say planetary scientist Sean Raymond and colleagues online March 5 in Monthly Notices of the Royal Astronomical Society.

“When I first came up with it, I thought it was ridiculous,” says Raymond, of the Laboratory of Astrophysics of Bordeaux in Floirac, France. “This model is kind of crazy, but it holds up.”

Rocky planets snuggled up to their suns are common in our galaxy. Many systems discovered by NASA’s Kepler space telescope have multiple planets — several larger than Earth — crammed into orbits smaller than Mercury’s. Though Kepler is biased toward finding scrunched-up solar systems, researchers wonder why there is a large gap between the sun and Mercury.

Scientists suspect that the inner planets of our solar system formed 4.6 billion years ago from a belt of debris that stretched between the current orbits of Venus and Earth. Mercury and Mars were built out of material along the edges of this belt, which explains why they are relatively small. Jupiter, traditionally thought to have formed much farther out, gets the blame for creating the belt’s outer edge. What shaped the inner edge has remained difficult to explain

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