Celestial Mechanics and Dynamical Astronomy

, Volume 69, Issue 1–2, pp 59–75

NEOs and Impacts: The Galactic Connection

  • W.M. Napier

DOI: 10.1023/A:1008318030411

Cite this article as:
Napier, W. Celestial Mechanics and Dynamical Astronomy (1997) 69: 59. doi:10.1023/A:1008318030411


The orbit of the solar system within the Galaxy is subject both to adiabatic tidal forces and to irregular buffeting caused by encounters with molecular clouds and spiral arms, while the long-period comet flux varies with the differential of these forces. Quasi-periodic episodes of Earth bombardment by Oort cloud comets are expected, with the half-period of the solar vertical oscillations being prominent. Various terrestrial datasets are examined and show evidence of a periodicity ∼27±1 Myr at a confidence level ≳ 99.5%, consistently with the expectations. Bombardment episodes thus appear to exert a controlling influence on global terrestrial processes. Conversely, the long-term terrestrial record provides an empirical constraint on the source regions of NEOs as well as on the dark matter content of the Galactic disc. During such episodes, climatic effects due to stratospheric dusting by very large comets are likely to be a major factor in geological and biological change.

Galactic tide Oort cloud cometary bombardment 

Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • W.M. Napier
    • 1
  1. 1.Armagh ObservatoryArmaghNorthern Ireland

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