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Here's looking at you, Triton - probably.

Here's looking at you, Triton--probably

The last major planetary body photographed during the Voyager 2 spacecraft's 12-year grand tour of the solar system most likely will be Neptune's big satellite Triton, late in August. The only major moon not clearly visible during the mission so far is Saturn's Titan, which is masked by a dense methane haze, but Earth-based observations have detected methane on Triton, too. Will the surface of this strange, backwards-orbiting satellite (the only one known around any major planet) pass unseen?

Scientists know little about Triton. Estimates of its diameter range from 2,200 to 4,800 kilometers, and its apparently steeply tilted axis may produce unusual seasonal variations in its atmosphere. John A. Stansberry, Jonathan I. Lunine and Martin G. Tomasko of the University of Arizona in Tucson note that the atmosphere's optical depth, essentially a measure of its opacity, is likely to have increased nearly tenfold since the first spectral observations of Triton in 1975, but probably not enough to hide its surface.

The optical depth is expected to have changed from 0.06 in 1975 to 0.6 by 1990, the year after Voyager's flyby, because Triton's south polar cap will be pointed directly at the sun. By comparison, the optical depth of the Martian atmosphere is typically about 0.02, suggesting that the optical depth during the Triton encounter will be "not large enough to obscure the surface, but large enough that it may be measurable by Voyager's cameras."
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Title Annotation:Voyager 2 spacecraft may photograph Neptune's satellite
Author:Eberhart, Jonathan
Publication:Science News
Date:Mar 25, 1989
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