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No. 95: Sep-Oct 1994

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Snowballs in hell?

Arecibo radar image of Mercury's morth pole
Arecibo radar image of Mercury's morth pole showing several craters.
In SF#79, we revealed that anomalous radar reflections from Mercury's polar regions might be due to residual deposits of water ice. At first, this possibility seems most unlikely given Mercury's proximity to the sun. Where the sun's rays beat directly on Mercury's surface, the temperature can reach 700K. Even glancing sunlight, occurring when the sun is perched on Mercury's horizon, should heat the surface to 170K. At this temperature, water ice would evaporate quickly in Mercury's near-vacuum atmosphere. But any permanently shaded areas at the planet's polar caps -- say, deep in a crater -- would remain below 100K. This is cold enough to retain ice, even in a vacuum.

Radar topographic studies of Mercury's polar regions, using the Jet Propulsion Laboratory's Goldstone antenna with the VLA (Very Large Array) plus the big Arecibo antenna in Puerto Rico, have been able to confirm that there are indeed craters in the polar regions of Mercury. These craters match up well with the radar reflectivity anomalies recorded earlier. So, it now seems likely that ice does exist on Mercury. And, since our moon also boasts permanently shadowed crater areas, ice probably survives there, too. This is good news for future lunar colonists.

But where could the ice on Mercury and the moon have come from? One source might have been the gases seeping out from the bodies' interiors. Also, cometary impacts could have added water vapor to the atmospheres. This would then have been deposited as frost in cold crater bottoms, just like the frost seen on winter window panes.

(Harmon, J.K., et al; "Radar Mapping of Mercury's Polar Anomalies," Nature, 369:213, 1994.)

Comment. But are comets really the water bearers the astonomers say they are? See the item under ASTRONOMY.

From Science Frontiers #95, SEP-OCT 1994. 1994-2000 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