Cometary impacts, molecular clouds, and the motion of the sun perpendicular to the galactic plane

ABSTRACT Raup and Sepkoski1 have presented evidence from marine fossils for a 26-Myr periodicity in the occurrence of mass extinctions. Using the same data Rampino and Stothers2 obtained a

different period, 30±1 Myr, which agrees with the 33±3-Myr half-period for the vertical oscillation of the Solar System about the plane of the galaxy3. To explain this agreement they

suggest2 that encounters with molecular clouds perturb the Sun's family of comets, causing many to enter the inner Solar System where one or more collide with the Earth; the cloud

encounter rate is modulated at twice the oscillation frequency, because the number density of clouds peaks at the galactic plane at the midpoint of the solar oscillation crossed by the Solar

System twice per period. Notwithstanding an apparent objection to this that the most recent extinctions are not in phase with the solar oscillation4, their model, given its stochastic

nature, can accommodate a few events with large phase discrepancies. The degree of modulation is crucial: it depends on the scale height of the population of molecular clouds relative to the

amplitude of the solar motion and tends to zero if this ratio is large and encounters are entirely random. Here we present data from CO surveys of molecular clouds both within and beyond

the solar circle, which permit explicit calculation of the strength of the modulation. The cloud layer near the Sun is too extended and, as a consequence, the modulation of cloud encounters

is too weak for a statistically significant period to be extracted from the nine extinctions analysed by Rampino and Stothers. Access through your institution Buy or subscribe This is a

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IS OSCILLATING Article 20 February 2024 A PLANETARY COLLISION AFTERGLOW AND TRANSIT OF THE RESULTANT DEBRIS CLOUD Article 11 October 2023 CHANGE IN THE EARTH–MOON IMPACTOR POPULATION AT

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J._ 276, 182–203 (1984). Article  ADS  CAS  Google Scholar  Download references AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Goddard Institute for Space Studies, 2880 Broadway, New York,

New York, 10025, USA Patrick Thaddeus * Columbia Astrophysics Laboratory, Department of Physics, Columbia University, New York, New York, 10027, USA Patrick Thaddeus & Gary A. Chanan

Authors * Patrick Thaddeus View author publications You can also search for this author inPubMed Google Scholar * Gary A. Chanan View author publications You can also search for this author

inPubMed Google Scholar RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Thaddeus, P., Chanan, G. Cometary impacts, molecular clouds, and the motion of

the Sun perpendicular to the galactic plane. _Nature_ 314, 73–75 (1985). https://doi.org/10.1038/314073a0 Download citation * Received: 28 October 1984 * Accepted: 20 December 1984 * Issue

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