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Science 21 June 2002:
Vol. 296. no. 5576, pp. 2151 - 2153
DOI: 10.1126/science.1072609
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Perspectives

PLANETARY SCIENCE:
Where Have All the Comets Gone?

Mark E. Bailey

The majority of comets that reach the inner solar system originate in the Oort cloud. However, models describing the dynamical evolution of such comets predict far more comets in short-period orbits than are observed. In his Perspective, Bailey discusses the implications of a more refined model (Levison et al.) that still predicts a surfeit of observed "Halley-type" comets relative to observations, and which concludes that the majority of Oort cloud comets disrupt into invisibly small fragments. This and other suggestions to account for the cometary "missing mass" are discussed. While important clues are being gathered, the coupled physicodynamical evolution of comets presents an intriguing puzzle.

The author is at the Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK. E-mail: meb{at}arm.ac.uk

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Science. ISSN 0036-8075 (print), 1095-9203 (online)