Best of 2010: The Death of Nemesis: The Sun's Distant, Dark Companion

In July, scientists said the data that once suggested the Sun is orbited by a distant dark companion now raises even more questions

Over the last 500 million years or so, life on Earth has been threatened on many occasions; the fossil record is littered with extinction events. What’s curious about these events is that they seem to occur with alarming regularity.

The periodicity 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?

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