Our Sun, in its youth some 4.5 billion years ago, ‘stole’ Planet Nine from a passing star system, says a team of European astronomers led by Lund University scientist Alexander Mustill.
Simulated structure of the hypothetical ice giant Planet Nine. Image credit: Esther Linder / Christoph Mordasini.
“It is almost ironic that while astronomers often find exoplanets hundreds of light-years away in other star systems, there’s probably one hiding in our own backyard,” Dr. Mustill said.
“Stars are born in clusters and often pass by one another. It is during these encounters that a star can steal one or more planets in orbit around another star. This is probably what happened when the Sun captured Planet Nine.”
In a computer-simulated model, Dr. Mustill and co-authors have shown that Planet Nine was probably captured by the Sun “when coming in close contact while orbiting another star.”
“We investigate how the Solar System might have come to host a wide-orbit eccentric body such as Planet Nine, a class of object we refer to as Novenitos,” they wrote in a paper in the Monthly Notices of the Royal Astronomical Society Letters (arXiv.org preprint).
“We show that it is indeed possible for the Sun to have captured such a planet from another star in a close encounter in its birth cluster.”
According to the astronomers, Planet Nine may very well have been ‘shoved’ by other planets, and when it ended up in a wide orbit around its host star, our Sun may have taken the opportunity to capture it.
“When the Sun later departed from the stellar cluster in which it was born, Planet Nine was stuck in an orbit around the Sun,” they said.
“It requires a lot more research before it can be ascertained that Planet Nine is the first exoplanet in our Solar System.”
If the theory is correct, Dr. Mustill and co-authors believe that “the study of space and the understanding of the Sun and the Earth will take a giant leap forward.”
“This is the only exoplanet that we, realistically, would be able to reach using a space probe,” Dr. Mustill said.
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Alexander J. Mustill et al. 2016. Is there an exoplanet in the Solar System? MNRAS 460 (1): L109-L113; doi: 10.1093/mnrasl/slw075
