Upper Limits for Condensed O2 on Saturn's Icy Satellites
and Rings
J. R. Spencer
Icarus 136, 349-352.
Preprint available in postscript form, including
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Abstract:
New 4800-7200 A spectra of Saturn's rings, and the icy Saturnian
satellites Enceladus, Tethys, Dione, Rhea, and Iapetus, do not show
the weak 5773 and 6275 A absorption bands due to high-density
condensed O2, that are seen, with a maximum depth of 1.8%, on
Ganymede's trailing side. The 5773 A band depth must be < 0.6%
(and very probably < 0.3%) on the rings, Tethys, Dione, Rhea, and
the trailing side of Iapetus, and < 1.2% on the trailing side of
Enceladus. The lack of detectable absorption does not rule out
abundant O2 molecules that are too well-separated to produce these
absorption bands. The observations show that the presence of O3,
recently detected on Rhea and Dione (Noll et al. 1997b) , does not
require the presence of detectable quantities of high-density O2. I
discuss the implications of the new observations for models of O2
formation on Ganymede.
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