A ROGUE star may have ploughed through our solar system in the distant past. It would have shaken up the outer reaches and could explain the peculiar properties of the icy bodies which orbit in the Kuiper belt.
These balls of ice, up to a few thousand kilometres across, inhabit the region between Uranus and Neptune. Most of the planets orbit in the same plane, that of the proto-planetary disc from which they were formed. But many Kuiper belt objects, including Pluto, travel in 鈥渉igh-inclination鈥� orbits, at a sharp angle to the plane of the planets.
Alice Quillen and Eric Blackman of the University of Rochester, New York, and David Trilling of the University of Pennsylvania speculated that the orbits could be explained by another star passing through the solar system, wreaking havoc as it went, so they investigated the idea using computer simulations.
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They found that if a star about a fifth of the sun鈥檚 mass approached the sun roughly perpendicular to the plane of the planets, and within 50 times the distance of the Earth to the sun, then about 30 per cent of the Kuiper belt objects would be scattered into high-inclination orbits. The rest of the solar system would be relatively undisturbed.
In a paper submitted to Astronomical Journal, the researchers suggest that the interloper probably came from the star cluster in which the sun was formed, and that the close encounter would have occurred within a billion years of the birth of the solar system.