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No. 4: July 1978

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What caused the grooves on phobos?

Photographs from the Viking Orbiters show that the Martian satellite Phobos displays a heavily grooved surface. Enough high-resolution photos have been taken to prove that these grooves emanate from the large crater named Stickney and run around the satellite to its opposite side where they die out. This suggests that the origin of the crater and the grooves are related. Further, the widest and deepest grooves (700 meters wide and 90 meters deep) are located close to Stickney. On the other side of Phobos, grooves are consistently less than 100 meters wide. Despite these hints of impact origin, the grooves are not quite what one would expect from simple fracture by collision. Some show beaded or pitted structures. Other grooves are composed of irregularly bounded segments. Finally, some of the straight-walled sections seem to have slightly raised rims. Evidently, some internal forces, perhaps stimulated by the formation of Stickney, also played a part.

(Thomas, P., et al; "Origin of the Grooves on Phobos," Nature, 273:282, 1978.)

Reference. The grooves of Phobos and its other anomalies are catalogued at ALL2 and ALL3 in The Moon and the Planets. To order this book, go to: here.

Map of the strange grooves on the Martian moon Phobos
Map of the strange grooves on the Martian moon Phobos

From Science Frontiers #4, July 1978. 1978-2000 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