A star grazed our solar system 70,000 years ago, and the first humans probably saw it

Some distant objects in our solar system bear the gravitational imprint of a small star’s close flight 70,000 years ago, when modern humans already roamed the Earth, according to a new study.

In 2015, a team of researchers announced that a red dwarf called Scholz’s Star had apparently grazed the solar system 70,000 years ago, approaching within a light-year of the sun. For perspective, the sun’s closest stellar neighbor these days, Proxima Centauri, is about 4.2 light-years away. Astronomers came to this conclusion by measuring the motion and speed of Scholz’s star – which zooms in space with a smaller companion, a brown dwarf or “failed star” – and extrapolating back in time .

Scholz’s star passed through the solar system at a time when the first humans and Neanderthals shared the Earth. The star likely appeared as a faint reddish light to anyone looking up at the time, the researchers of the new study said. [Top 10 Star Mysteries]

The new study bolsters the 2015 analysis with a different kind of evidence. A research team led by Carlos de la Fuente Marcos, of the Complutense University of Madrid, analyzed 339 known bodies in the solar system with hyperbolic orbits – V-shaped paths in space, rather than circular or elliptical.

An artist’s illustration of the red dwarf known as the Star of Scholz, with its brown dwarf companion in the foreground, during the pair’s flight over the solar system 70,000 years ago. The sun would appear as a bright star of the pair (left background). (Image credit: Artist’s concept of Scholz’s Star)

Objects in hyperbolic orbits could theoretically have originated from interstellar space, as could ‘Oumuamua, the first known visitor to the solar system born around another star. But they could also be natives pushed on strange tracks by gravitational interactions with the sun or some of its planets. And the inhabitants of the Oort Cloud – a frigid ring far from the sun that is home to billions of comets – could even be “disturbed” by the Milky Way’s disk or stray stars getting too close.

“Using numerical simulations, we calculated the radiators or the positions in the sky from which all these hyperbolic objects seem to come”, de la Fuente Marcos said in a press release.

“In principle, one would expect these positions to be evenly distributed across the sky, especially if these objects originate from the Oort cloud,” he added. “However, what we find is very different: a statistically significant accumulation of radiant heat. The pronounced overdensity appears to be projected in the direction of the constellation Gemini, which corresponds to the close encounter with the star of Scholz.”

“Oumuamua is not in the Gemini group, so this bizarre needle-shaped object really does appear to be from another star system,” the researchers added. They also reported eight other bodies that could be interstellar intruders, including comet ISON, which shattered during a much-anticipated close passage of the sun in November 2013.

The new study was published online last month in the journal Monthly notices from the Royal Astronomical Society: letters. You can read it for free on the arXiv.org online preprint site.

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Arline J. Mercier