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No. 79: Jan-Feb 1992

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Mercury's polar caps and icy minicomets

Mercury, closest planet to the sun, should be baked bone dry, seeing that equatorial temperatures reach 800F. When Mariner 10 flew past Mercury in 1974, its camera eye reinforced the baked-cinder model. To everyone's surprise, recent radar images obtained with powerful earth-based antennas, revealed a highly reflective patch at Mercury's north pole. Could it be ice, for ice reflects radar waves well? Quite possibly, for when Mercury's polar temperatures are calculated, away from the sun's direct glare, they plunge to -235F. This means that some of the water vapor in the planet's thin atmosphere might freeze out in the poles, creating ice or frost caps.

Wouldn't Mariner 10 have seen such a remarkable deposit? Not necessarily, for the spacecraft viewed only half the planet and, if the 640 x 300-kilometer ice patch were covered with dust, it could have been invisible to the camera. But it would still be a bright patch on terrestrial radar scopes, because radars see through thin dust layers.

So, polar ice is not physically impossible on Mercury, although it is defi nitely surprising so close to the sun. All that is needed is a little water in the planet's atmosphere. Mainstream thinking is that "passing comets and asteroids" might bequeath Mercury some of their H2O cargos. (Cowen, R.; "Icy Clues from Mercury's Other Half," Science News, 140:295, 1991.) Also: Wilford, John Noble; "Photographs by Radar Hint of Ice on Poles of Mercury," New York Times, p. A14, November 7, 1991. Cr. J. Covey)

Comment. What the above references do not mention is the possibility that the requisite water vapor for the formation of Mercury's polar caps might come from a steady rain of icy minicomets. L. Frank has suggested that 100-meter icy minicomets continuously pepper solarsystem planets. They might even have contributed to the formation of the earth's oceans. Icy comets are anathema here on earth and are equally detestable at Mercury's orbit.

From Science Frontiers #79, JAN-FEB 1992. 1992-2000 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