Nemesis Reconsidered

In 1984, Raup and Sepkoski found a 26 million year periodicity in the timing of terrestrial extinctions over the last 250 million years. Nowadays, the data is much better. We re-examined the data, using two different fossil data sets to look for simultaneous, in-phase signals. We found one, exactly where it should be, at 27 My. (The time series for geological stages has expanded 3% in the time period RS examined.) Furthermore, it is highly regular--too regular for the orbit of Nemesis, a dark companion of the Sun hypothesized to induce the extinctions. Calculations showed Nemesis should have an orbit which varied substantially due to orbital perturbations--and the time series analysis shows highly stable results. More detail can be found in a Wired Science news story or in the original paper published in Monthly Notices of the Royal Astronomical Society and in arXiv.

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