“Planet X” lost in space?

Where is Planet X? It may have escaped the solar system or may not exist at all, say fossil researchers. (Credit: Ben McGee)

Researchers at the University of Kansas and the Smithsonian Institute have performed one of the most extensive analyses of Earth’s past extinction patterns to date.  So, what did researchers Adrian Melott and Richard Bambach conclude?  Planet X cannot exist.

Planet X, also known as Nemesis, is a proposed “dark” (i.e. dim) companion star to the sun, such as a red dwarf or brown dwarf, that sits at an extreme distance and orbits once every 26-million years or so (see other related Planet X blogs here and here).  Conventional Nemesis theory holds that as Nemesis is knocked around by the gravity of nearby stars in the galactic plane, the dark star perturbs the Solar System’s Oort cloud, a shell of icy fragments surrounding the solar system, and sends a shower of comets into the solar system, causing impacts and ultimately – extinctions.

The problem that Melott and Bambach found is that:

1. According to galactic gravity fields, Nemesis cannot have an exceedingly stable orbit,
2. The extinction patterns in the fossil record are too regular to be caused by something orbiting the way Nemesis would.

The Solar System moves up and down through the galactic plane as it orbits the Milky Way, carrying the Earth and other planets, (and Nemesis if it is there) along with it.  Well, this up-and-down motion can be roughly measured and tells us that the Solar System passes through the galaxy’s plane less than twice every 54-million years.  If true, that means a perturbation of the Oort cloud because of Nemesis interacting with the galactic plane once every 27-million years doesn’t line up quite right.

This difference was brought into sharp relief by Melott and Bambach, who measured the regularity of fossil record extinctions with meticulous detail using multiple methods, and they found that the period of extinctions is too sharp.  They suggest looking for alternate mechanisms to explain these surprisingly regular apocalyptic events.

So, is Planet X gone?  Another possibility is that we lost it.

If Nemesis’s orbit were too unstable, being perturbed by nearby stars as the Solar System passes through the galactic plane, (think having someone push you regularly on a swingset,) eventually it achieves an escape trajectory and becomes “unbound” – a rogue star in the galaxy no longer gravitationally-linked to us.

In that case, we’d never know – a free dwarf star in the interstellar medium is extremely difficult for astronomers to find.  (i.e., currently impossible.)

So, in an ironic twist, has the Nemesis theory been destroyed by the extinction record that engendered it?

Only time will tell.