Terrestrial catastrophism—Nemesis or Galaxy?

Abstract

The ∼30 Myr periodicity associated with the Sun's motion through the central plane has been linked to geomagnetic reversals^1,2, biological extinctions³ and crater ages^4–6. This periodicity is consistent with galactic theories of terrestrial catastrophism^1,5. It has been suggested, however, that the periodicity is controlled by a hypothetical stellar companion of the Sun (‘Nemesis’) in a highly eccentric orbit of arbitrarily chosen period which periodically upsets the Oort cloud^7,8. Although the idea appears superficially attractive, there has been little or no attempt to relate it to what is already known about the Oort cloud and the environment in which the Sun–Nemesis system would have to exist. Thus, the inferred phase of the Nemesis cycle is inconsistent with such evidence as there may be for a recent disturbance (∼5 Myr) of the Oort cloud, namely the apparent non-equilibrium distributions of perihelia¹ and 1/a (ref. 9) and the enhancement of the short-period comet population^10,11 (compare ref. 12). It also discounts the generally high glacial, magnetic and orogenic activity on Earth within this period and the Sun's recent passage through Gould's belt^10,13. However, the most serious problem is reconciling the approximately constant time-averaged cratering rate for the last ∼3,000 Myr (ref. 14) and the stability of the proposed system.