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No. 62: Mar-Apr 1989

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DANCING TO THE COMETS' TUNE

"When planetary scientists examine one kind of meteorite rich in iron, the H-chondrites, they find that the meteorites' ages do not spread evenly through time. Instead, the ages seem to cluster at 7 and 30 million years."

Astronomers have hitherto been content to attribute these clumped ages to collisions among the meteorites' parent bodies - the asteroids - which ply periodic orbits. However, S. Perlmutter and R.A. Muller, at Berkeley, point to the apparent 26- to 30-million-year periodicities of three terrestrial phenomena:

  1. Biological extinctions in the fossil record,
  2. Magnetic field reversals, and
  3. Terrestrial-crater ages.

Could there be a connection between the clumped meteorite ages and these terrestrial phenomena? Perlmutter and Muller propose that all of these phenomena are the consequence of periodic storms of comets that invade the inner solar system from the direction of the Oort Cloud of comets that purportedly hovers at the fringe of the solar system. These comets not only devastate the earth but also collide with the asteroids, knocking off those bits and pieces we call meteorites.

(Anonymous; "Do Meteorite Ages Tell of Comet Storms?" Astronomy, 17:12, January 1989.)

Comment. Unanswered above is the question of why comet storms should be periodic. One hypothesis is that Nemesis, the so-called Death Star, a dark companion of our sun, lurks out there, periodically nudging the Oort Cloud of comets, causing it to release some of its comets.

From Science Frontiers #62, MAR-APR 1989. � 1989-2000 William R. Corliss