|Date:||8/30/01 11:26:15 PM Pacific Daylight Time|
The link on your site pertaining to the Nemesis hypothesis goes to an article written by someone who was not very familiar with the topic. You will note that Dr. Richard Muller of UC Berkeley is given rather short shrift in the article, which fails to note that Muller is the author of the Nemesis hypothesis. Indeed, he wrote a book about how it came about, entitled Nemesis: The Death Star, which detailed how he and his colleagues, including the redoubtable Dr. Louis Alvarez, his mentor, and Alvarez's son (the father-son team gave us the asteroidal/cometary impact theory for the dinosaur's extinction, as you will recall) developed the hypothesis during the last 16 years. A couple of other scientists located on the East Coast sent a draft of a paper noting the 26 million year extinction cycle to the senior Alvarez for comment. Alvarez, being very busy, as always, passed it on to Muller to analyze and shoot it down (Alvarez regarded their discernment of a 26 million year extinction cycle as erroneous and ludicrous). Muller surprised, and, at first, angered Alvarez by telling him that he thought the other two guys were onto something. To Alvarez' credit, once Muller showed him why he thought the scientists were right, Alvarez turned completely around and later supported Muller's efforts to find an explanation for the cyclic extinctions, with the explanation being that our solar system is really binary in nature, with the second star being a red or brown dwarf which orbits Sol, disturbing the Oort cloud, as discussed briefly in the article. Muller's book is very good and goes far beyond the Nemesis hypothesis itself, discussing how the Alvarezes developed their theory and how all of the ancillary theories came to be. It is a fascinating, well-written book. It is out of print now, but can probably be found in the UW science libraries or in a used book store. Muller is a guy to watch on the Big Science front.
I don't mean to quibble, but I just saw your inclusion of my letter to you (anonymous - thank you!) under a note which seems to say that Nemesis is theorized to approach within 1 light year of Sol at time of Oort cloud perturbation. Actually, in Muller's book, he says that the furthest away the dwarf star gets is about 3.5 light years or 14 trillion miles (which is roughly where it is now, give or take a trillion miles, as we are 15 million years away from the next close approach), and that the closest it gets is about one half a light year or 2.935 trillion miles away. The Oort Cloud is said to range from about that distance to a full light year all the way around the solar system in all directions (i.e., forming a globe around the Solar System which starts about a half a light year out and continues for another half a light year).
The effect of a dwarf star going through the Oort Cloud was calculated by Muller to dislodge about a billion comets which would head inside the Earth's orbit toward the Sun (at the rate of about 1,000 per year for the million years that Nemesis was closest to the Sun in its orbit), making for pretty spectacular night skies every 26-30 million years (the orbital frequency of Nemesis is said to be affected by the gravitational influences of other objects [chiefly, stars], which accelerates or retards its speed, resulting in a certain amount of deviation from the 26 million year cycle). Anyway, these calculations are necessarily guesswork since Nemesis has not yet been located with telescopes and were based upon educated estimates by Dutch astrophysicist Piet Hut when he was visiting Berkeley. Hut specializes in orbital dynamics. He postulated what he said was a "typical orbit" for a companion star with an elliptical eccentricity of 0.7, an egg-shaped orbit. But use of the term "guesswork" is not meant to be taken disparagingly or lightly, as Hut's guesswork in this area is a good deal better than most people's careful calculations and is based on long experience addressing these kinds of problems. Just as a comet or spacecraft will do, Nemesis speeds up along its egg-shaped orbit as it nears and whips around the Sun, slowing as it approaches its furthest point away from the Sun. Even at its closest point, and even if it were a red dwarf, beings on Earth would only see it as another faint star in the heavens. If it were a brown dwarf, they would not even see that much.
Once one has gone through these calculations, it does not seem remarkable that there are massive extinctions every 26 million years but, rather, that on two occasions since the Permo-Triassic extinction event 250 million years ago, there were no extinction events on the 26 million year cycle. On those two occasions, living things on Earth lucked out, the comets and meteors missed the planet and there were no great cataclysms when Nemesis came to town. But, 80% of the time, life was almost totally extinguished as a side effect of Nemesis' advent (keeping in mind, of course, that there are other, more minor but still significant, extinction cycles which are not Nemesis-driven which can also be discerned in the geologic record). The Permo-Triassic extinction event wiped out over 90% of all life on Earth, even deep marine life, and holds the record so far as we know for the worst extinction event in the history of life on this planet.
It has been calculated that Nemesis' orbit stands a pretty good chance of remaining stable for at least one billion years (this figure is less useful when one discovers that we do not know when the billion years began). Before then, the best conclusion physicists can offer is that Nemesis was even closer to the Sun with the consequences to Earth being even more cataclysmic in terms of cometary impacts. So, at no point do Muller and his colleagues appear to believe that Nemesis passed as far away as one light year at its closest point. The distance is said to be about half that. Do you have newer information than the above?