The universe is a dangerous place. A new analysis has revealed that stars can frequently steal planets from each other in high-speed fly-bys 鈥� something that may even have happened in our own solar system.
Our understanding of how planets form was developed by looking out at our own cosmic neighbourhood, but these explanations can鈥檛 account for some of the other star systems we have discovered, such as Jupiter-like planets orbiting extremely close to low-mass stars.
鈥淭here are a number of different observations that suggest that there is more going on than just standard formation theory,鈥� says Rosalba Perna at Stony Brook University in New York.
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Perna and her team used computer simulations to investigate what happens when neighbouring stars have a close encounter. They found that inside dense clusters of stars, fly-bys frequently wreak havoc on planetary systems, destroying, ejecting or even stealing planets away from their hosts about once every billion years per system.
That may not sound like much, but multiplied by the huge number of stars in a cluster, it becomes a frequent occurrence. This could explain some of the strange exoplanets we have discovered, as gas giants like Jupiter might be born around sun-like stars but later seized during encounters with incoming low-mass stars, as suggested by a related paper by the same authors.
We might be able to find such stolen planets by searching for those on lopsided orbits that don鈥檛 match the plane of their host star, says Eric Ford at Pennsylvania State University.
The work could also have relevance closer to home. The solar system formed over millions of years among a dense cluster of about 2000 other stars. That means there could have been an additional planet ripped away from the sun during its early years.
鈥淚t鈥檚 absolutely possible that the solar system had, at some point, more planets or fewer planets, but it鈥檚 something we just have no way to know any more,鈥� says Perna.
It is also possible that our sun has been pilfering planets, says Ford. 鈥淎nother system may have swapped a planet into our own, a yet undiscovered planet in the far reaches of our solar system.鈥�
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