Another Star May Have Skimmed the Solar System 70,000 Years Ago

Our solar system has just the one star, but astronomers now have good reason to think a second star paid us a visit about 70,000 years ago. That’s when Scholz’s Star is believed to have skimmed the edge of our solar system on its way out to deep interstellar space. Scholz’s Star is a small red dwarf, but it may have passed so close by that our early human ancestors could have seen it when they looked up at the sky.

Scholz’s Star is actually a low-mass binary system consisting of a red dwarf and a brown dwarf. Red dwarfs are the most common type of star in the universe, and brown dwarfs are one step below that. They’re sometimes called “failed stars” because they don’t have enough mass to fuse hydrogen and become a “real star.” They can probably fuse some other elements, so you can think of them as very large, warm Jupiters. Our first hint that Scholz’s Star buzzed the solar system came in 2015 when a team of astronomers calculated its path. This binary pair is zipping through space rather fast, and the analysis projected a path through the edge of our solar system.

A new study from researchers at the Complutense University of Madrid has found more evidence to support a visit by Scholz’s Star. A team led by Carlos de la Fuente Marcos analyzed 339 objects in the outer solar system known to have hyperbolic orbits — that means they have V-shaped paths instead of circular or elliptical ones. These objects could theoretically be captured from interstellar space, but they could also be native to the solar system (likely from the Oort Cloud, a cocoon of comets around the solar system). A passing star could have nudged them into unusual orbits, and that’s what the researchers were trying to find out.

You’d expect objects with hyperbolic orbits in the outer solar system to be randomly distributed, but that’s not the case. There is a “statistically significant” concentration of such objects in the direction of the constellation of Gemini. That fits with the proposed path of Scholz’s Star 70,000 years ago.

Scholz’s Star is currently between 17 and 23 light years away. At its closest approach, it may have been just one light year away from the sun. Currently, Proxima Centauri is our closest celestial neighbor at 4.5 light years distant. Early humans living at the time would have seen a faint red spot in the sky. It’s possible Scholz’s Star could have knocked comets out of the Oort Cloud as it passed, and those objects could pose a danger to the inner solar system. It’ll take about 2 million years for those objects to reach us, though.