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Scientists Discover Closest Flyby Ever of Alien Star

Feb 18, 2015 03:27 PM EST

Scientists have discovered the closest flyby ever of an alien star, which passed within a light-year of the Sun some 70,000 years ago and nearly invaded our solar system.

Today, the star known as WISE J072003.20-084651.2, or Scholz's star, is 20 light-years away from us in the constellation Monoceros. But according to a new study published in Astrophysical Journal Letters, it didn't always keep its distance.

A group of astronomers from the US, Europe, Chile and South Africa recently found that this dim star, its brown dwarf companion and our solar system once had a close encounter of a third kind. It passed right by us at a distance of about 0.8 light-years (8 trillion kilometers, 5 trillion miles, or 52,000 astronomical units), moving through the comets in the outer reaches of the Oort Cloud that surrounds our solar system. No other star is known to have come that close.

In fact, its approach was five times closer than the current closest star, Proxima Centauri, which sits 4.2 light-years away.

Scholz's star is a small, dim red dwarf that is so faint (50 times fainter than normal, to be exact) that it cannot be seen with the naked eye. However, it is magnetically active and can "flare" thousands of times brighter for a brief period of time. So, lead study author Eric Mamajek, of the University of Rochester, suggests that due to a rare flaring event our ancestors 70,000 years ago may have seen the star's near-miss of our solar system.

This star first caught the eye of Mamajek and his colleagues because of its trajectory, which appeared to be moving directly away from us at incredible speed, despite the fact that it was fairly close by. To calculate its relative motion, the researchers used observations from the Southern African Large Telescope and the Magellan Telescopes in Chile.

"Sure enough, the radial velocity measurements were consistent with it running away from the Sun's vicinity - and we realized it must have had a close flyby in the past," Mamajek said in a press release.

This discovery also resulted in some good news for our solar system, which apparently has to worry about alien flybys. Last year, a different group of astronomers reported that a "rogue star" called HIP 85605 was going to come dangerously close to us 240,000 to 470,000 years from now. However, now Mamajek and his colleagues say this prediction was way off, and HIP 85605 won't come anywhere near that close. It seems that once again our solar system dodged a bullet... or a star, rather.

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