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The Question

(Submitted November 30, 1996)

Do you have any new information on the Nemesis Star,the so called companion star to our Sun ?

The Answer

To recap the story of Nemesis (see, e.g., 1990 October issue of Scientific American): in 1984, Raup & Sepkoski claimed that mass extinctions, like the one that killed the dinosaurs 65 million years ago, occurred every 32 million years. Since the favored theory for the demise of dinosaurs is an asteroid or cometary impact, the periodicity would suggests some mechanism to disturb the comets in the Oort cloud every 32 million years. Richard Muller and others hypothesized that a faint companion star, nicknamed Nemesis, that orbits the Sun every 32 million years, could explain this.

However, many geologists are not convinced that mass extinctions are periodic, so they see no need for such a star. Nevertheless, Muller and colleagues have embarked on the difficult search for a possible, dim companion to the Sun. The most recent report I could find on this was a conference paper from 1994 (Carlson et al 1994 in "New Developments Regarding the KT Event and Other Catastrophes in Earth History", Houston Univ., p19-20). Here are some sentences off the abstract: "Unfortunately, standard four-color photometry does not distinguish between red dwarfs and giants. ... Every star of the correct spectral type and magnitude must be scrutinized. ... We are currently scrutinizing 3098 fields, which we believe contain all possible red dwarf candidates in the northern hemisphere. ... The software is now completed and we are eliminating stars every clear night." I presume the search is still on-going but have not yielded a positive detection.

A good description and more references can be found at: (

You may also want to check out the article in the 1990 October issue of Scientific American

Koji Mukai and Eric Christian
with help from Drs. Chen, Loewenstein and Snowden
for Imagine the Universe!

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