|The Nemesis theory does not tie in with 2012 predictions|
|Artist's impression of Nemesis|
The Nemesis Theory
Nemesis is a hypothetical red dwarf or brown dwarf star, orbiting the Sun at a distance of about 50,000 to 100,000 AU. This object was originally postulated to exist as part of a hypothesis to explain a perceived cycle of mass extinctions in the geological record.
Origin of the theory
The "Nemesis Theory" was an outgrowth of the claim of Alvarez et al., that the impact of a large (>10 km diameter) comet or asteroid was responsible for the great mass extinction that took place 65 million years ago.
Studies of the fossil record by palentologists Dave Raup and Jack Sepkoski shows that this was not an isolated event, but one of several mass extinctions that appear to occur on a regular 26 million year cycle. Their original paper analyzed marine fossil families, and was published in the Proceedings of the National Academy of Science USA, vol 81, pages 801-805 (1984).
Critiques of the theory
- The "regular" mass extinctions were never "regular" at all. In fact, there is really no periodicity to the data. Using much the same data that was available to Raup and Sepkoski, you get variance from the 26 million year cycles, with some occurring much sooner and others far longer than "average".
- Astronomers can show that the predicted effect, that of Nemesis disturbing the Oort Cloud and causing a "rain of comets" which produced the extinctions, could have occurred from the many "close passes" or "near misses" by the many stars in our Sun's neighborhood. As a demonstration of this, in about 10,000 years, Barnard's Star will cozy up to our Sun's Oort Cloud. Will this red dwarf cause a mass extinction? No one knows, but it is certainly a possibility, without any Nemesis existing at all.
- Neither a red dwarf nor brown dwarf companion has ever been detected for our Sun, even though IR surveys have detected brown dwarf stars as far away as 20 light years.
Nemesis is a classic example of a compelling hypothesis designed to fit data, which later turned out to be all in error. Originally, the concept of "regular" mass extinctions could not be satisfactorily explained by biologists, so palentolgists Raup and Sepkoski, seeing a 26 Million year period, suggested that the cause be "non-terrestrial".
After this, some astronomers, assuming that Raup and Sepkoski knew what they were talking about, merely connected the dots, plotting an estimated orbit for Sol's "undetected companion", hypothesizing that if the last extinction was 5 million years ago, then "Nemesis" would have to be "out there" some 1-1.5 light years away.
But maybe, just maybe…
As Michael Emmert points out in the comments blow, there is just a tiny sliver of a chance that some nemesis-like object may yet exist out there, undiscovered. If it exists at all, it would have to be big, at least 5 MJ1 and perhaps up to 25 MJ. However, as Mike points out, it would also not be due back for millions of years.