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Envisioning the waters of Phobos.

Envisioning the waters of Phobos

Does water lie frozen inside the tiny Martian moon Phobos? Scientists have many reasons to think there used to be a substantial amount of it, say Fraser P. Fanale and James R. Salvail of the University of Hawaii in Honolulu, who now suggest that perhaps some of the water remains.

Spectrally, Phobos resembles the class (C) of asteroids that appear similar to a group of meteorites called carbonaceous chondrites. Their compositions include varying amounts of water, and some show signs of having undergone "intensive alteration by liquids," the scientists note in the April GEOPHYSICAL RESEARCH LETTERS. Using estimates of how much water Phobos had when it formed and how much heating the satellite might have experienced during its history, Fanale and Salvail calculated how much water might remain in it and attempted to determine how far below the surface and how widely spread the water lies, probably in form of ice.

Allowing for a wide variation in the number and sizes of the pores in Phobos' rock, the researchers conclude that the depth of the ice layer's top probably ranges from "a few tens to a few hundreds of meters" over much of the satellite. For example, halfway from the equator to each of the satellite's poles -- a latitude of 45[deg.] north and south -- the temperature at the top of the pemanently frozen layer is about 225 kelvins. In the equatorial zone, the top of the ice would probably lie no lower than about 1 kilometer. And near the equator, no water may remain -- unless water originally made up about one-fifth of the satellite's mass -- because heat from variouis sources would have driven it off.

Fanale was one of several U.S. scientists invited to take part in the Soviet Phobos project, which was to carry out elecromagnetic sounding of the satellite's depths from orbit, among other tasks. The Soviets lost communications with the Phobos 2 craft before its landers could be deployed. But they may soon announce results obtained before the craft fell silent -- perhaps including spectra gathered from orbit that might reveal the presence of water.
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Publication:Science News
Date:May 6, 1989
Words:354
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