The Nemesis theory postulates that every 26 to 30 million years, life on Earth is severely jeopardized by the arrival of a small companion star to the sun. Dubbed “Nemesis” (after the Greek goddess of retribution), the companion star”through its gravitational pull”unleashes a furious storm of comets into the inner solar system that lasts anywhere from 100,000 years to two million years. Of the billions of comets sent swarming toward the sun, several strike the Earth, triggering a nightmarish sequence of ecological catastrophes. This theory has been abandoned since 2011, and a fairly recent study shows that Nemesis himself would destabilize the 3 last planets-Saturn, Uranus, and Neptune. Nemesis would make our solar system a binary star system. A binary star is a star system consisting of two stars orbiting around their common center of mass.  Binary stars are often detected optically, in which case they are called visual binaries. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. 

An international team of astrophysicists has shown that planetary systems with very distant binary stars are particularly susceptible to violent disruptions, more so than if they had stellar companions with tighter orbits around them.

Unlike the Sun, many stars are members of binary star systems – where two stars orbit one another – and these stars’ planetary systems can be altered by the gravity of their companion stars. The orbits of very distant or wide stellar companions often become very eccentric – ie. less circular – over time, driving the once-distant star into a plunging orbit that passes very close to the planets once per orbital period. The gravity of this close-passing companion can then wreak havoc on planetary systems, triggering planetary scatterings and even ejections. 

This movie shows two simulations of planetary system disruption by galactic disturbances to wide binary stars. On the left is a zoomed-out view showing the orbit of a hypothetical 0.1 solar mass binary star around our own solar system with an initial orbital separation of 10,000 AU (1 AU is the distance between the Earth and the sun). On the right is a zoomed-in view of the orbits of Jupiter, Saturn, Uranus, and Neptune. As the binary orbit becomes eccentric, this eventually excites the planetary orbits and Uranus and Neptune are both ejected while Saturn, now severely destabilized, will become a dark, frigid hulk, devoid of any form of life.

Simulation of wide binary stars planetary disruption00:14

Simulation of wide binary stars planetary disruption

With Nemesis gone, the best explanation for these extinctions would be the gravity of passing stars or Jupiter nudging asteroids out of their orbits into the inner Solar System.

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