Sun's Dark Companion 'Nemesis' Not So Likely

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."

Comments

period of passing through the galaxy ecliptics?

[Kvasio]

isn't this the most simple explaination? Most stars in Mily Way arms are known to bounce up and down the ecliptic.

Re:period of passing through the galaxy ecliptics?

[evilviper]

isn't this the most simple explaination? [sic]

No, the most simplest explanation is that it's all an imagined phenomenon. A statistical anomaly due to selection bias, miscalculation, or vastly incomplete data-set... A ghost. Occam's Razor says so.

Re:period of passing through the galaxy ecliptics?

[jc42]

The sun doesn't just orbit the center of the galaxy, though. It also moves up and down relative to the galactic plane. Some have suggested that whenever the solar system reverses direction in that oscillation, very bad things happen, ...

That's close to a conventional explanation, but off by 1/4 cycle. The extreme high/low points of the solar system's bobbing orbit are outside the galactic plane, and would be the low-danger points. The rough parts of the (approx. 60 million year) cycle are the two crossings through the central part of the galactic plane, which are the densest portions. During the crossings, the solar system is zipping through the galactic plane at a few hundred km/s, producing lots of collisions with whatever rubble happens to be there.

Part of the explanation from the astronomers who've done the studies is that, although we're about in the middle of the galactic plane right now, we're actually in a "Local Bubble" about 300 light years across, so there's not much galactic rubble in the solar system right now. There are low-density bubbles like this scattered around, the results of things like supernova explosions in the distant past.

Stick around for another million years or so, and we'll exit the local bubble. There might be some nice fireworks then, and perhaps another mass extinction.

Of course, we are going through a mass extinction event right now, but it's an unusual one with a known causative agent that's not astronomical. It seems that a new top-level predator has recently evolved, which has been devastating the ecosystem all over the planet. This will probably confuse the paleontologists in the future, since they'll see a mass extinction during a crossing of the galactic plane, but won't see any evidence at all of the impact that presumably caused it. They'll also see the evidence of a species with high intelligence, but of course that couldn't be the cause, because you wouldn't expect a highly-intelligent species to destroy its own ecosystem, right? So the extinction event will remain a mystery.

Second comment debunks

[Xtifr]

The second comment under the article seems to be a pretty serious debunking. I'm not going to take sides or tell you who's right and wrong because I don't know, but I will note that arXiv (the source for the claims) is for pre-prints and is not peer-reviewed.

Re:How long since last time

[cheesee]

From FTA:

There is a smidgeon of good news. The last extinction event in this chain happened 11 million years ago so, in theory at least, we have plenty of time to work out where the next catastrophe is coming from.

Re:How long since last time

[anorlunda]

Better still, read the comment to the article by Torbjorn at the same URL as the article. Torbjorn calls it "Bad research, worse article" and he makes a pretty strong case.

BadAstronomer said something similar

[magsol]

...only it was a larger multiple: somewhere in the vicinity of every 150-180 million years. However, in this case, it's due to our solar system's z-axis oscillation with respect to the rest of the Milky Way galaxy. The dust and gas of the galaxy acts as a shield against cosmic radiation, but every 150-180 million years, our solar system reaches the z-edge of the galaxy and is maximally exposed to the elements.

What accounts for the 5-7 other mass extinctions within that time frame, however, I defer to TFA.