NEOs and Impacts: The Galactic Connection |
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Authors: | WM Napier |
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Institution: | (1) Armagh Observatory, College Hill, Armagh, BT61 9DG, Northern Ireland |
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Abstract: | 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.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Galactic tide Oort cloud cometary bombardment |
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