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No. 69: May-Jun 1990

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Mystery Of The Missing Comets

A key feature of our solar system is the Oort Cloud of comets that surrounds the sun and its family of planets. No one has yet seen the Oort Cloud directly, but the textbooks say that it must be there. In fact, all stars like our sun with planetary systems should have their own private Oort Clouds of comets - if the prevailing theory of planetary-system formation is correct. When we see a comet looping around the sun, it is because it has been jostled loose from the Oort Cloud by a passing star or molecular cloud. Further, some of these jostled comets should be kicked outwards and thus escape the solar system. Continuing with this reasoning, we on earth should sometimes see interstellar comets that have been shaken loose from other stellar systems. But we don't! T.A. McGlynn and R.D. Chapman worry about this.

"This lack of detections of extrasolar comets is becoming an embarrassment to the theories of solar system and comet formation."

McGlynn and Chapman calculate that we should have seen six interstellar comets in the past 150 years, but the actual number is zero. Such interstellar comets would be easy to spot because they would be moving much faster than our own comets. Two possible explanations for the missing interstellar comets are: (1) The Oort Cloud theory is wrong; and (2) Solar systems like ours are rarer than supposed.

(Anonymous; "Mystery of the Missing Comets," Sky and Telescope, 79:254, 1990.)

Comment. See SF#64 for musings about Halley's comet being an alien interloper.

Reference. More on missing short- period comets can be found in ACO6 in our catalog: The Sun and Solar System Debris. Ordering details here.

From Science Frontiers #69, MAY-JUN 1990. 1990-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987