TravisTR passes along a story about the death of Nemesis. "The data that once suggested the Sun is orbited by a distant dark companion now raises even more questions... The periodicity [of mass extinctions] is a matter of some controversy among paleobiologists but there is a growing consensus that something of enormous destructive power happens every 26 or 27 million years. The question is what? ... another idea first put forward in the 1980s is that the Sun has a distant dark companion called Nemesis that sweeps through the Oort cloud every 27 million years or so, sending a deadly shower of comets our way. ... [Researchers] have brought together a massive set of extinction data from the last 500 million years, a period that is twice as long as anybody else has studied. And their analysis shows an excess of extinctions every 27 million years, with a confidence level of 99%. That's a clear, sharp signal over a huge length of time. At first glance, you'd think it clearly backs the idea that a distant dark object orbits the Sun every 27 million years. But ironically, the accuracy and regularity of these events is actually evidence against Nemesis' existence."