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No. 85: Jan-Feb 1993

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Heavy traffic in near-earth space

That region of outer space near the earth carries a heavier load of flotsam and jetsam than scientists expected. The devastation of the 1908 Tunguska impact in Siberia warns us that this space debris -- meteors, comets, asteroids -- is an active threat. A recent spate of articles paints an ominous future.

The earth's retinue of mini-asteroids.

"Asteroids as big as houses pass near the Earth 100 times more often than anyone suspected. On an average day, about 50 asteroids measuring at least 10 metres across come closer to the Earth than the Moon, and each year about five such objects may hit the planet." (Second reference below.)

These startling data come from D. Rabinowitz and coworkers at the University of Arizona, who have been scanning nearby space with a telescope fitted with supersensitive charge-coupled devices (CCDs). They have picked up astronomical objects that have escaped conventional instruments. Several sources have been suggested for this unexpected, threateningly large population of small asteroids: (1) debris hurled earthward from collisions within the asteroid belt located between Mars and Jupiter; (2) the breakup of a large object formerly in orbit about the earth; and (3) fragments blasted off the moon by impacts of large asteroids there. (Kerr, Richard A.; "Earth Gains a Retinue of Mini-Asteroids," Science, 258: 403, 1992. Also: Mitton, Simon; "HouseSized Asteroids Home In on the Earth," New Scientist, p. 16, October 31, 1992.)

Comet Smith-Tuttle. At a conference in Sydney last October, astronomer D. Steele announced that comet SmithTuttle is heading towards a possible impact with earth on August 14, 2116. This 3.1-mile-diameter chunk of ice would have the destructive power of 20 million megatons (1.6 million Hiroshima bombs). (Anonymous; "Astronomer Predicts Comet Collision," Baltimore Sun, October 26, 1992.)

Some recent meteorite impacts. Turning from the dire consequences discussed above, just what sort of astronomical debris actually does hit the earth on a day-to-day basis? Fist-sized meteorites strike our planet about every two hours. These are the ones we read about in the newspapers; and they have left a surprisingly large legacy of damage to human structures. C. Spratt and S. Stephens, in a survey published in Mercury in 1992, listed 61 verified meteorite strikes since 1790 in which buildings and other human works were damaged. (Of course most fell harmlessly in the sea and unpopulated areas.) Spratt and Stephens also provide a table of 26 nearmisses of humans plus one confirmed human impact. At least one horse and a dog have been killed by meteorites. These lists make engrossing reading, but we cannot take the space to reproduce them here. (Spratt, Christopher, and Stephens, Sally; "Against All Odds," Mercury, 21: 50, March/April 1992.)

From Science Frontiers #85, JAN-FEB 1993. 1993-2000 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