Nemesis

Nemesis is a theoretical second sun in our solar system, a dwarf star named after the Greek goddess of vengeance. In the English vocabulary, the word nemesis has come to mean downfall or ruin, and surely nothing good can result from a celestial body bearing this moniker. According to one theory, Nemesis will indeed bring about our ruin one day by setting in motion an extinction event that will wipe us off the face of the Earth.

Proponents of the Nemesis theory say it has happened before. In fact, every 26-28 million years, the Earth has a little problem. Some horrible and mysterious catastrophe brings about mass extinction, destroying a large percentage of life on the planet and altering the balance of nature.