Alien Intruder: The Star That Passed Through Our Solar System


There is talk about the Sun’s evil twin, aptly named Nemesis. This hypothesis was forwarded by scientist Richard Muller in 1983 as an explanation for the quasi-regularity with which mass extinctions occur on Earth.

He believed that our star’s invisible dance partner completed a revolution around the Sun once every 26 million years. We’re unable to see it because it’s a tiny brown dwarf that emits too little light for us to be able to detect. Once every 26 million years, Nemesis would reach its perihelion (the point in its orbit when it gets closest to the Sun) and perturb comets in the Oort Cloud.

Obviously, that would piss off the comets that would in turn head toward the center of our solar system. One or some of them would collide with Earth and BOOM! extinction.

While this theory is both scary and interesting, it hasn’t gained much traction with the scientific world. Nonetheless, many believe in the existence of Nemesis and are probably looking for it, scanning the night skies with squinty eyes.

But while Nemesis remains unproven, a team of astronomers from the European Space Observatory and the University of Rochester believe our very own solar system received a visit from an alien star and it wasn’t all that long ago. The close (in astronomical terms) encounter happened 70,000 years ago, right around the time when The Young and the Restless aired its first episode. There’s little chance our ancestors saw it (the star, not the episode) since it’s a red dwarf and therefore quite faint.

The astronomers nicknamed it Scholz’s star presumably because they grew tired of typing its official name: WISE J072003.20-084651.2.



Sorry, wrong star!


Luckily, the spherical intruder didn’t have the balls to get all up in our Sun’s grille and maintained a safe distance of around 0.8 light years, merely passing through the Oort Cloud. But since the solar system ends at the outer limit of the Oort Cloud, Scholz’s star’s trajectory counts as a valid pass through the solar system so the title of the article wasn’t misleading.

Since we’re hellbent on giving you all the details, we should note that Scholz’s star is actually part of a binary star system and it’s on pair with a brown dwarf. But since brown dwarfs are usually referred to as “failed stars” we’ll say no more. Shame on it for not having enough mass to fuse hydrogen.

So, how exactly did astronomers figure out that the red dwarf had trespassed our solar neighborhood?

Scholz’s star is not a new discovery since it’s been photographed in the past. However, the sheer number of stars guarantees that not all of them are examined. This is why it went unnoticed until astronomers began measuring the distance to the stars that showed up in the photos. They found out that WISE J072003.20-084651.2 was located around 20 light years away and wasn’t moving very fast across the firmament.

Wanting to determine whether it was moving away from or toward us, the sky-watchers employed some astronomical wizardry in the form of Doppler shift measurements. Eric Mamajek, associate professor of physics and astronomy at the University of Rochester can take it from here:

Most stars this nearby show much larger tangential motion. 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,” said Mamajek.

The astronomers crunched the data provided by spectrograph readings from large telescopes in South Africa and Chile. Taking into account multiple variables, such as the star’s position, distance and velocity, plus the gravitational field of the Milky Way and ran 10,000 simulations of the star’s orbit. Based on the results, they can say with a 98 per cent certainty that Scholz’s star passed through the Oort Cloud.

This star came and passed and we’re still here. But there might be others heading for us as we speak (protip: don’t panic, it takes them a long time). That’s when the ESA’s recently launched Gaia spacecraft comes into play. During the following years, Gaia is expected to set its eye on more than a billion stars and we’ll know if we’ve had other visitors or if more are coming.

Blessed be the great mother!

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