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Dynamical constraints on the mass and perihelion distance of Nemesis and the stability of its orbit


It has been suggested1,2 that the observed periodic extinction of species at intervals of 26 Myr (ref. 3) may be catalysed by a hypothetical stellar companion of the Sun, Nemesis, with an orbital period of 26 Myr. The passage of a stellar companion through the inner comet cloud4 will fill the loss cone of these comets and cause a comet shower to enter the planetary system. It has been estimated that about 20–30 comets will hit the Earth during a shower, which lasts less than a million yr. Such Earth impacts would produce considerable environmental stress and may lead to widespread extinction of species4. I now investigate the effect of Nemesis on the comets in the inner comet cloud. This is used to determine the minimum required mass of Nemesis and its minimum required perihelion distance. The effect of passing stars on the stability of the orbit of Nemesis is investigated, and the probability of its having passed within the planetary system estimated.

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Hills, J. Dynamical constraints on the mass and perihelion distance of Nemesis and the stability of its orbit. Nature 311, 636–638 (1984).

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