Nemesis for Nemesis?

The issue of the theoretical stability of the Nemesis orbit has been settled, but most astronomers don't know the answer. Actually, they think they know the answer, but they are incorrect. As the 19th century humorist Josh Billings said, "The trouble with most folks isn't so much their ignorance. It's know'n so many things that ain't so." I can guide you to the origin of the confusion.

Look at Nature Vol 311, Oct 18, 1984. You will find a host of articles on the stability of the Nemesis orbit. In addition, you will find an editorial comment by Mark Bailey (on page 602), entitled "Nemesis for Nemesis."

The articles are as follows:

1. J. G. Hills (page 636) analyzes the stability of the Nemesis orbit. He supports the Nemesis hypothesis and calculates some details. He speculates that Nemesis may be responsible for the eccentric orbit of Pluto. (Hills was the theorist who originally recognized the possibility of comet showers.)

2. Piet Hut (page 638) does the most complete and definitive analysis of the Nemesis orbit. He concludes that the results given in the original Nemesis paper are verified: the orbit has a stability time constant of about one billion (10^9) years. This means that the remaining life of the orbit is a billion years. When the solar system was created 4.5 billion years ago, the Nemesis lifetime would have been about 5.5 billion years, and we have used up 4.5 of those. The 10^9 year stability implies that the present orbit is not perfectly periodic, and this is verified by a careful examination of the extinction data. Hut shows that the Nemesis orbit is stable only if it is near the plane of the Milky Way. (Hut is now a fellow at the Institute for Advanced Study at Princeton.)

3. Torbett and Smoluchowski (page 641) conclude that passing giant molecular clouds would make the Nemesis orbit unstable. However they neglect the fact that these massive clouds are very diffuse; later work (D. Morris and R. Muller, Icarus v. 65, p. 1-12) show that these clouds actually have no effect on the orbit stability.

4. Mark Bailey wrote an editorial review (page 602) entitled "Nemesis for Nemesis," in which he says, "the Nemesis proposal is extended and shown, in fact, to be quite incapable of producing the strictly periodic sequence for which is was originally designed." This is a misinterpretation of the original Nemesis paper (Nature vol 308 pp 715-717, 1984). We never expected a perfectly periodic signal in an orbit that had only a 10^9 year lifetime. Bailey goes on to characterize Hut's paper as "a near retraction"!!!! Hut considered his paper to be a vindication of the original Nemesis paper. He contacted Bailey to find out how Bailey could be so wrong in his understanding, and Bailey told Hut that he never wrote those words! "Near retraction" had been inserted by the editor at Nature!

Bailey also refers to a paper by Clube and Napier, in which they show that the Nemesis orbit has a stability of 10^9 years. But Clube and Napier then conclude that this rules out the Nemesis theory, rather than realizing that this stability is exactly what we had said in our original paper. Apparently they never realized (as did Hut) that the expected lifetime of Nemesis is linear, not exponential, so that that the present stability is not the same as the stability 4.5 billion years ago.

But now for the fascinating sociology of science. I have talked to many astronomers since 1984, and the majority of them believe that the Nemesis theory was ruled out, because the orbit turned out to be unstable. In most of these cases I could track down the origin of their opinion. Frequently the opinion had been obtained from someone else -- often the local planetary scientist. But in every case, the ultimate origin was the altered article by Mark Bailey in Nature.

Why is this? Because Bailey summarized the three articles -- there was no need for a busy scientist to read the actual papers. I never found an expert (i.e. someone that others depended on for their opinion) that had actually read the Hut article. Why bother, when it amounts to a "virtual retraction"?

The trouble with most folks, isn't so much their ignorance ....

At the time, Piet and I thought we would find Nemesis soon, so he decided not to write a letter to the editor complaining about the error in the Bailey summary.

That's half the story of why Nemesis is not believed. The other half is that we predicted we would find it within a few years, and we haven't. So most people think our search found no such star. In fact, the search stalled soon after it started. There is no reason to believe that Nemesis is not the solution to the mystery of the periodic extinctions, and there is no alternative theory that has survived scrutiny.