The nature of near-Earth meteor streams from comets

Following the embarrassing failure of the predicted return of a Leonid meteor storm in 1998 following the return of the parent comet, Tempel-Tuttle, a dozen groups of astronomers set out to solve the problem of predicting future meteor storms. The first success in history was achieved in 1999, when three of the groups predicted the time and place correctly to within ten minutes. These three successes were all based on the meteor stream concept, and the idea that comets release a new meteor stream at every return to perihelion. However, of the three successes, only the Lyytinen prediction based on the Van Flandern comet model got the meteor rates correct to within a factor of two. The next-best model by Asher & McNaught was off by a factor of eight. Continued success was achieved in 2000 and 2001, when the Earth again encountered various Leonid meteor streams released from the comet centuries ago. The Lyytinen-Van Flandern predictions were again closest, and that model was the only one to correctly predict an outburst of the Ursids in December 2001. This shows that the model is general enough to apply to other comets and meteor streams, and does not need a history of observed encounters to set various adjustable parameters as the other models do. In all, eight shower or storm peaks have now been predicted correctly. This tells us about the nature of comets, about how meteor streams in the inner solar system evolve over time, and about hazards in the near-Earth environment associated with these now-predictable meteor storms.