A recently discovered star sailed through the outer fringes of our solar system, astronomers say, the closest a star has ever come to us -- but don't worry, they say, it happened around 70,000 years ago.
A team of astronomers from the United States, Chile and South Africa says the star likely passed through the Oort Cloud, a distant cloud of comets, a fly-by that saw it pass within just 0.8 light years of us.
In cosmic terms, that's almost a close shave, they say; our nearest neighbor star, Proxima Centauri, is a comfortable 4.2 light years away from us.
The low-mass star, dubbed "Scholz's star," caught astronomers' attention because despite being fairly close in astronomical terms, just 20 light years away, it displayed very slow motion across the sky, known as tangential motion, the scientists report in the Astrophysical Journal Letters.
"Most stars this nearby show much larger tangential motion," says study lead author Eric Mamajek, a professor of astronomy and physics at the University of Rochester. "The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had 'recently' come close to the solar system and was moving away."
Further observation confirmed it was running almost directly away from the vicinity of our solar system, "and we realized it must have had a close flyby in the past," Mamajek says.
To plot its past trajectory, astronomers used observations of the star's current velocity gathered by the Southern African Large Telescope and the Magellan telescope at Chile's Las Campanas Observatory.
While the close flyby of Scholz's star likely had little impact on the Oort Cloud -- a star passing within the inner regions of the cloud could trigger a "comet shower" sending space rocks into the inner solar system -- Mamajek suggests that "other dynamically important Oort Cloud perturbers may be lurking among nearby stars."
The Gaia satellite, recently launched by the European Space Agency and capable of mapping the position and velocity of a billion stars, may tell us about other stars that had a close encounter with our solar system in the past or might in the far future, the astronomers say.
Scholz's star, one partner in a binary system, is a low-mass red dwarf with a "brown dwarf" companion.
Brown dwarfs are thought of as "failed stars," with masses too low to initiate hydrogen fusion in their cores to become a star, but still much more massive than gas giant planets like Jupiter, astronomers explain.
The red dwarf is named for its discoverer, Ralf-Dieter Scholz of the Leibniz-Institut für Astrophysik Potsdam in Germany, who detected it in 2013.
