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Tar sands on Iapetus.

Tar sands on Iapetus

One of the solar system's most unusual-looking moons is Saturn's "two-faced" Iapetus, icy-bright on the side that faces behind as the satellite circles in its orbit, but darkened on the "leading" hemisphere by some unidentified material about 10 times less reflective. Now a researcher says spectral measurements of the dark side resemble those of tar sands on Earth.

Tar sands, according to Edward A. Cloutis of the University of Alberta in Edmonton, consist of clays, bitumen (a complex array of variously polymerized hydrocarbons), quartz grains, water and lesser amounts of a few other minerals. After studying tar-sand samples from northeastern Alberta, consisting of viscous, organic material embedded in sediments, Cloutis reports in the July 14 SCIENCE that the best match for the dark-side spectrum of Iapetus is a mixture of 90 percent clay and 10 percent coal tar representing organic material.

Still, he notes that neither the specific clay-coal tar mixture nor the tar sand in general provides a perfect spectral match for Iapetus' dark stuff. An iron-substituted clay "seems to be a necessary component," he says, and other materials--such as some amount of a highly polymerized hydrocarbon--improve the spectrum. For now, Iapetus remains an enigma.
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Title Annotation:Space Sciences
Publication:Science News
Date:Jul 22, 1989
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