In a somewhat strange new finding, an international group of astronomers has been able to determine that roughly ~70,000 years ago our solar system had a close encounter with an alien star system.

So close, in fact, that the “dim star” in question actually passed through the outer reaches of our solar system — making its way through the outer Oort Cloud, where most long period comets spend most of their time.

As it stands, this is the closest known approach by a foreign star that modern researchers are currently aware of — roughly 5 times closer then the closest star now known of, Proxima Centauri. The dim star in question has been nicknamed by the researchers as “Scholz’s star”.

A research paper detailing the finding was just published in Astrophysical Journal Letters — where the specifics of the work are explained in detail.

A recent press release from the University of Rochester provides further information:

The star’s trajectory suggests that 70,000 years ago it passed roughly 52,000 astronomical units away (or about 0.8 light years, which equals 8 trillion kilometers, or 5 trillion miles). This is astronomically close; our closest neighbor star Proxima Centauri is 4.2 light years distant. In fact, the astronomers explain in the paper that they are 98% certain that it went through what is known as the “outer Oort Cloud” – a region at the edge of the solar system filled with trillions of comets a mile or more across that are thought to give rise to long-period comets orbiting the Sun after their orbits are perturbed.

The star originally caught Mamajek’s attention during a discussion with co-author Valentin D. Ivanov, from the European Southern Observatory. Scholz’s star had an unusual mix of characteristics: despite being fairly close (“only” 20 light years away), it showed very slow tangential motion, that is, motion across the sky. The radial velocity measurements taken by Ivanov and collaborators, however, showed the star moving almost directly away from the solar system at considerable speed.

“Most stars this nearby show much larger tangential motion,” stated lead author Eric Mamajek from the University of Rochester. “The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had ‘recently’ come close to the solar system and was moving away. Sure enough, the radial velocity measurements were consistent with it running away from the Sun’s vicinity – and we realized it must have had a close flyby in the past.”

In order to determine the star’s exact trajectory, the researchers required both tangential velocity and radial velocity. These data points were obtained via Doppler shift — using measurements obtained by the Southern African Large Telescope (SALT) in South Africa; and the Magellan telescope at Las Campanas Observatory in Chile.

When all the data points were put together it became clear that Scholz’s star was traveling away from the solar system — the researchers then traced its position back in time to a position ~70,000 years ago when it was likely closest to our Sun (as per their models).

During the 10,000 simulated orbits for the star that the researchers did — incorporating data accounting for position, velocity, distance, the Milky Way’s gravitational field, and statistical uncertainties — 98% portrayed the star as having passing through the outer Oort cloud. Out of all 10,000 simulated orbits, only one showed the star as having passed through the inner Oort Cloud — which would have likely triggered changes to the orbit paths of comets in the vicinity (perhaps leading to new meteor showers).

Currently, Scholz’s star is a small, dim red dwarf in the constellation of Monoceros, about 20 light years away. However, at the closest point in its flyby of the solar system, Scholz’s star would have been a 10th magnitude star – about 50 times fainter than can normally be seen with the naked eye at night. It is magnetically active, however, which can cause stars to “flare” and briefly become thousands of times brighter. So it is possible that Scholz’s star may have been visible to the naked eye by our ancestors 70,000 years ago for minutes or hours at a time during rare flaring events.

An interesting thought. People have very likely always been interested to some degree or other in what’s going on in the nights sky — and, for that matter, some animals (such as the dung beetle) actually use the light gradient of the Milky Way to navigate at night with. So that fascination with the stars certainly isn’t unique to people.

The star is part of a binary star system: a low-mass red dwarf star (with mass about 8% that of the Sun) and a “brown dwarf” companion (with mass about 6% that of the Sun). Brown dwarfs are considered “failed stars;” their masses are too low to fuse hydrogen in their cores like a “star,” but they are still much more massive than gas giant planets like Jupiter.

The official designation of the star, for those interested, is “WISE J072003.20-084651.2” — worth nothing is that it was actually only first discovered just back in late 2013.

Those looking for more information can find the original research paper here.

(Those interested in related subjects will probably enjoy this article as well: Rogue Extrasolar Planet Discovered, Free-Floating Planet Discovered Only 100 Light Years Away)

Image Credit: Michael Osadciw/University of Rochester