70,000 Years Ago, Another Star Flew by the Edge of the Solar System

70,000 Years Ago, Another Star Flew by the Edge of the Solar System
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Proxima Centauri, the closest star outside the Solar System, currently rests 4.24 light years away, but it won't always be our nearest cosmic neighbor.

The reason for this is simple, and much to the dismay of fortune-telling astrologists: Stars move. In roughly 27,000 years, Proxima Centauri will be just three light years away from the Sun, after which it will gradually move away. 6,000 years after that, Proxima Centauri will no longer be the closest star, its title superseded by Ross 248, which, at its closest, will be just 3.024 light years from the Sun.

But long before Proxima Centauri and Ross 248 started duking it out to be our next door neighbor, the Sun may have had a much more intimate stellar partner.

According to an international team of astronomers, about 70,000 years ago a red dwarf star -- nicknamed "Scholz’s star" for the astronomer who discovered it -- passed by our solar system just 0.8 light years distant. In fact, 98% of the 10,000 simulations the team ran projected that the star's path grazed the outer edges of the Oort Cloud, a region of space filled with icy planetesimals which marks the final boundary of our solar system.

If the astronomers' analysis, which was recently published to The Astrophysical Journal Letters, is correct, that would make Scholz’s star the closest known star to ever pass by our solar system.

Eric Mamajek, an astronomer and physicist at the University of Rochester and lead author of the study, grew curious about Scholz’s star during a discussion with Valentin Ivanov, from the European Southern Observatory. Ivanov, a co-author, noted that the star wasn't really moving across the sky. Subsequent analysis revealed that the star was actually moving directly away from the solar system at breakneck speed, like a thief fleeing the scene of a crime. Focusing the Southern African Large Telescope (SALT) and Chile's Magellan telescope at the star eventually produced enough data to resolve the star's prior path. 

Though Scholz’s star would have been a very close neighbor, our ancient ancestors probably wouldn't have noticed it. The red dwarf star is just 8% the mass of the sun and much dimmer. Even at its nearest, the star would have been fifty times too faint to be seen with the naked eye at night. However, since Scholz’s star is magnetically active, it may have occasionally flared up to become thousands of times brighter, making it just barely visible for a meager span of minutes or hours per event.

Scholz’s star is now twenty light years away and won't be returning anytime soon. However, Dr. Coryn Bailer-Jones of the Max Planck Institute for Astronomy calculates that we may receive another visitor in the distant future. Last December, Baller-Jones reported that the rogue star HIP 85605 may pass as close as .132 light years to the solar system between 240,000 and 470,000 years from now. That's a close miss on the cosmic scale, but more than far enough that our futuristic ancestors will have little to worry about. The only concern would be that HIP 85605's foray through the inner Oort Cloud might send a few comets careening in Earth's direction.

Mamajek and his co-authors doubt Bailer-Jones' claims. They calculate that HIP 85605 won't approach closer than 300 light years away, leaving Scholz’s star's "closest" title uncontested for the time being.

(Image: Michael Osadciw/University of Rochester)

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