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[49.03] Ice chemistry on the Saturnian satellites

M.L. Delitsky, A.L. Lane (JPL)

The magnetosphere of Saturn contains plasma ions that have flows inwards and outwards of the planet, as measured by Voyager. These ions impact the satellites and induce chemistry in their surfaces. Voyager measured such species as O⁺, H₂O⁺ (and other water group ions), N⁺, N₂⁺, H⁺ and others, as well as electrons. If N⁺ and N₂⁺ ions from Titan sputtering reach the inner satellites Rhea, Dione, Tethys, Enceladus and Mimas, implanting of these ions into the water ice surfaces should induce a complex nitrogen oxides chemistry. Species observed in laboratory experiments of N⁺ impact into water ice include NO, NO₂, NO₃, HNO₂, HNO₃, NH₂OH, HNO, NH, and NH₂. Impact of N₂⁺ will yield N₂O, HNNO, and N₂. If the surfaces also include CO₂ (which is a possible volatile already observed on the Jovian satellites), then other species that may be formed as a result of N⁺ impact into H₂O/CO₂ ice will be HNCO, NCO and R-OCN. The simplest molecule, NO (nitric oxide), should have an appreciable vapor pressure at Saturnian satellite temperatures. At 90 K (a typical temp for Saturnian satellites), the vapor pressure of NO is about 4 millibar. At 105 K, its v.p. would be 98 millibar. This should be observable with high-resolution instruments.

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