PerspectivePlanetary Science

Where Have All the Comets Gone?

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Science  21 Jun 2002:
Vol. 296, Issue 5576, pp. 2151-2153
DOI: 10.1126/science.1072609

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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.