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Alien Star Missed Us by Less Than a Light-Year, Scientists Say

Astronomers say a red dwarf star and its brown dwarf companion passed within a light-year of our own sun 70,000 years ago, moving through the comets in the outer reaches of the Oort Cloud that surrounds our solar system.

The star is known as WISE J072003.20-084651.2, or Scholz's star. Today, it's 20 light-years away from us in the constellation Monoceros. But in a study published by Astrophysical Journal Letters, researchers say it passed right by us at a distance of 5 trillion miles (8 trillion kilometers, or 52,000 astronomical units, or 0.8 light-years). No other star has been known to come that close.

Scholz's star would typically be too faint to be seen with the naked eye from Earth, even during the close encounter. But the research team, led by the University of Rochester's Eric Mamajek, says there's a chance that our ancestors in Africa might have seen a magnetically induced flare-up.

Image: Scholz's star
An artist's conception shows Scholz's star and its brown dwarf companion in the foreground during its flyby of the solar system 70,000 years ago. The sun would have appeared as a brilliant star, seen here in the background at left. Scholz's star and its companion are now about 20 light-years away. Michael Osadciw / University of Rochester

Mamajek and his colleagues became interested in the star's trajectory after finding out that it appeared to be moving directly away from us — or toward us — at high velocity. They calculated its relative motion using 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 news release.

It's good news that Scholz's star missed us, but there's even better news: Last year, a different group of astronomers reported that a different star called HIP 85605 might make a dangerous pass through the Oort Cloud 240,000 to 470,000 years from now. Now Mamajek and his colleagues say HIP 85605 won't come anywhere near that close.

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In addition to Mamajek, the authors of "The Closest Known Flyby of a Star to the Solar System" include Scott Barenfeld, Valentin Ivanov, Alexei Kniazev, Petri Väisänen, Yuri Beletsky and Henri Boffin.