A Passing Star Shook Our Solar System 70,000 Years Ago
Back in 2015, astronomers first learned that a nearby star came within 0.8 lightyears of our own solar system about 70,000 years ago. During that initial discovery, it was assumed that there weren't any lasting effects.
But that's not the case - a new study published in Monthly Notices of the Royal Astronomical Society found some ways that a passing star (a red dwarf called Scholz's Star) did impact the fringes of our solar system, in ways that can still be seen to this day. Some objects in our solar system's Oort Cloud were thrown off their previous course due to the immense gravity of the star.
In hindsight, it makes sense. Considering the closest star to us right now is Proxima Centauri at 4.24 lightyears away, a star grazing us from less than a lightyear would scramble things a little bit. Scholz's star is currently 20 lightyears away, making it less of a danger now than it was 70,000 years ago.
The Oort Cloud is a group of icy bodies on the farthest edges of our solar system, well past Pluto and towards the end of the Kuiper Belt. Objects within the Oort Cloud would naturally be the closest to Scholz star when it passed by, and the new research looked at the red dwarf star's current position, along with a brown dwarf or "failed star" that travels with it, and extrapolated how close it came by our solar system so long ago.
And while doing that, they came across a number of Oort Cloud objects with exaggerated orbits (known as hyperbolic orbits) whose longterm trajectories matched up perfectly with a close stellar encounter in their past.
Most interestingly is that 70,000 years ago, early humans were wandering the Earth and could likely see Scholz's Star up in the night sky. For those early humans and Neanderthals who could see the star, it would have appeared as a bright red dot in the sky; not as big as the sun, but tough to miss as well.
About 70,000 years ago, when the human species was already on Earth, a small reddish star approached our solar system...— Mikko Kolkkala (@XCsci) March 21, 2018
Scholz's star https://t.co/RC8qxb84DA image: José A. Peñas pic.twitter.com/X4w0zEo91m
It is possible that these hyperbolically orbiting Oort Cloud objects got their trajectories in other ways, but it's unlikely. The best alternative explanation would be that they're interstellar objects, which travelled from a distant solar system to our own and entered in such a way that they're stuck in a bizarre orbit around the sun. But the only known interstellar object is the passing asteroid 'Oumuamua.
An alien star is thought to pass by our solar system every 100,000 years or so, although Scholz's Star came especially close. Either way, this isn't something will have to worry about for a few more tens of thousands of years.