“In another theory, planetary scientists suggested that one region of the solar system in particular, known as the Oort comet cloud, plays a key role in mass extinctions. The Oort cloud is a sprawling region at the border of our solar system that contains trillions of icy bodies. Muller put forth a popular hypothesis in the 1980s that said our sun has a sort of evil twin in the Oort cloud. This hypothetical star, he suggested, has an orbital cycle such that it would perturb its neighboring objects, and send 1 billion of them hurtling toward Earth every 26 million years. The star, a binary to the sun, was nicknamed Nemesis, and playfully referred to as the death star. ‘The binary star, or Nemesis theory, was an alternate to the Galactic-plane story,’ Rampino told me. ‘But the star was looked for, but never found, so Nemesis theory is out of favor now.’”