Hydrogen Sulfide on IO: Evidence from Telescopic and Laboratory Infrared Spectra

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Science  28 Apr 1989:
Vol. 244, Issue 4903, pp. 454-457
DOI: 10.1126/science.244.4903.454


Evidence is reported for hydrogen sulfide (H2S) on Io's surface. An infrared band at 3.915 (± 0.015) micrometers in several ground-based spectra of Io can be accounted for by reflectance from H2S frost deposited on or cocondensed with sulfur dioxide (SO2) frost. Temporal variation in the occurrence and intensity of the band suggests that condensed H2S on Io's surface is transient, implying a similar variation of H2S abundance in Io's atmosphere. The band was observed in full-disk measurements of Io at several orbital longitudes, including once at 24°(∼0.5 hour after Io's reappearance after an eclipse)—but not after another reappearance at 22°—and once at 95°(on Io's leading hemisphere). These results suggest that condensed H2S is sparse and variable but can be widespread on Io's surface. When present, it would not only produce the infrared band but would brighten Io's typical surface at ultraviolet and visible wavelengths.

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