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Transient star grazing our solar system 'just left,' cosmically speaking

The nearest star beyond our own sun is 4 light-years away, but not long ago (in terms of cosmic time) a small binary star system buzzed the edge of our solar system, coming five times closer to Earth.

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An artist's conception of Scholz's star and its brown-dwarf companion (foreground) during its flyby of the solar system 70,000 years ago. Michael Osadciw/University of Rochester

Our solar system often seems like a remote island floating in the immense empty ocean of space, but it turns out we do get some pretty heavyweight visitors every now and then.

Sure, sure, comets come to visit all the time these days, but a group of astronomers says it's determined that a small binary star system dubbed "Scholz's star" buzzed the edges of our solar system just 70,000 years ago. On the cosmic time scale, that's so recent that we could still practically wave goodbye from our front door.

At that point in history, there may have been both Neanderthals and anatomically modern humans wandering around. In fact, some believe that is right around the point in history when we were just starting to get our evolutionary act together, developing things like languages, tools and really slick cave paintings that descendants would totally dig for eons.

Unfortunately, those early ancestors probably weren't together enough to notice a binary star hanging out at the edge of the Oort cloud, which is a comet cluster of sorts that basically envelopes our solar system at the furthest reaches of the sun's gravity. (Oort does sound like the sort of name a stereotypical caveman society might dream up for such a concept, though.)

The transient star would have passed within about 52,000 astronomical units (1 a.u. = the distance between Earth and our sun) or 0.8 light-years of us, according to a paper published in Astrophysical Journal Letters.

To get a sense of how close that is, consider that the nearest star we know of today, Proxima Centauri, is 4.2 light-years away.

Scholz's star was only passing through, though. The binary system kept on the move and is now 20 light-years away.

As it moved through the Oort cloud, the star system may have agitated the trillions of small bodies believed to be drifting around out there, potentially showering the inner solar system with comets. Not exactly the best kind of visitor to have in the neighborhood.

Fortunately, work is beginning on a celestial neighborhood watch of sorts. The European Space Agency's recently launched Gaia satellite should be able to map the locations and velocities of a billion stars, which will give us a better sense of which ones have visited in the past or may be planning to swing by in the future.