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[24.06] Saturn's satellites: Predictions for Cassini

M.L. Delitsky (Jet Propulsion Laboratory), C.A. Hibbitts (Planetary Science Institute)

Saturn's satellites are subjected to a variety of energy inputs (from photons, magnetospheric and solar ions and electrons) which will affect their surface composition. The Saturn magnetosphere contains an assortment of ions, including O⁺ and H⁺ from sputtering of water ice on the inner satellites and N⁺ from sputtering of Titan's atmosphere. Implantation of these ions onto the surfaces of the satellites may produce compounds possibly detectable by Cassini instruments.

The satellites contain water ice and carbon dioxide ice (and possibly organics, on Phoebe). In Delitsky and Lane (2002), chemistry resulting from nitrogen ion implantation into water ice and carbon dioxide ice was outlined. From deposition of N⁺ ions into H₂O/CO₂, a complicated C-H-N-O chemistry may result, including formation of isocyanates, nitriles, nitrogen oxides and amino acids. Upon irradiation, H₂O/CO₂ mixtures will yield esters, ketones, alcohols, carboxylic acids and other interesting compounds. Cassini's infrared instruments CIRS and VIMS have spectral ranges that can detect many bands of these compounds. VIMS spectral range is ~ 0.35 - 5.1 microns; CIRS covers the spectral range ~ 7 - 100 microns, although its Mid-IR interferometer portion (7 -16 microns) is where organic materials are particularly spectrally active.

Weak features are present in the short IR for NO (1.91 microns), NO₂ (1.95), NH₃ (2.00, 2.24), CH₃OH (2.27, 2.34), and CO₂ (1.965, 2.01) [Quirico et al.,1999]. Some molecules have stronger absorption features at these wavelengths: [CO₂: 4.25 - 4.27 microns; NH₃: 3 microns and 9.2 microns (important because the 3 micron band can be masked by water); H₂CO₃: 3.88 microns (weak); HCOOH: 8.2 microns; O₂: ~9.7 microns]. These molecules may exist as ices, or as molecules trapped in the surface. CH- and CN-containing molecules absorb at 3.2 - 3.4 microns, and ~ 4.6 microns, respectively. H₂O₂, detected on Europa by its 3.5 micron band, may exist in the icy surfaces of the Saturn satellites as well.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.