[LINK] "Death Star Off the Hook for Mass Extinctions"

[rfmcdonald]

Going by this evidence, Sol is probably a solitary star after all, since without the periodic mass extinctions there wasn't any special reason to imagine that Nemesis existed at all. This just leaves one question: what does cause mass extinctions every 27 million years like clockwork?

A massive extinction like the one that claimed the dinosaurs has hit the Earth like clockwork every 27 million years, a new fossil analysis confirms. But the study claims to rule out one controversial explanation: a dark stellar companion called Nemesis that sends a regular rain of deadly comets toward Earth.

“The main astronomical ideas you can come up with that could cause something like this just don’t work,” said physicist Adrian Melott of the University of Kansas, a coauthor of the new study.

Nemesis was first suggested in 1984 as a way to explain an alarmingly regular series of extinctions in the marine fossil record, which was discovered by paleontologists David Raup and Jack Sepkoski. In light of the suggestion in 1980 that the dinosaurs were killed by a catastrophic impact, an invisible cosmic sniper lobbing comets at the inner solar system seemed like a plausible culprit.


Two independent groups of astronomers suggested that a dim brown dwarf or red dwarf star lying between one and two light years from the sun could throw a shower of ice and rock from the Oort Cloud every 26 million or 27 million years to wreak havoc on Earth. Because the orbit of this “death star” would be tweaked by interactions with other stars and the Milky Way, the time between one impact and the next should vary by 15 to 30 percent.

But now, Melott and coauthor Richard Bambauch of the National Museum of Natural History in Washington, DC, say that’s not actually what happens. The extinctions come almost exactly every 27 million years, they say, to a confidence interval of 99 percent.

“It’s really too good, it’s too sharp and fixed,” Melott said. “It’s like a clock.”