Laboratory Studies of Ammonia-Water Ice--Relevance to Outer Solar system Surfaces

Details Laboratory Studies of Ammonia-Water Ice--Relevance to Outer Solar system Surfaces Laboratory Studies of Ammonia-Water Ice--Relevance to Outer Solar system Surfaces

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p11d0804m&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P11D-0804

Other

6020 Ices, 6060 Radiation And Chemistry, 6224 Kuiper Belt Objects, 6270 Pluto And Satellites, 6280 Saturnian Satellites

Scientific paper

Water- and ammonia-ices have been observed or postulated as important components of the icy surfaces of planetary satellites and KBO objects in the outer Solar System. A feature in the near-infrared, near 2.2 microns, is attributed to NH3 in the spectra of Charon, Quaoar, and Miranda, a possible source being cryomagma brought up to cold surfaces where it is quenched. Models used to fit the data include the presence of ammonia hydrates. These observations, along with some evidence for NH3 ice on Enceladus, lead to the prediction that NH3 is one of the more abundant species incorporated into outer Solar System bodies. Significant gaps exist in our knowledge of the spectra of solid water and ammonia mixtures, the formation of NH3-hydrates, and the stability of these ices for relevant physical conditions. The role of thermal processing and exposure to different particle radiation environments has not been investigated. Therefore our laboratory study has examined the influences of composition, formation temperature, thermal- and radiation-processing, on the spectra of both pure NH3 ice and various H2O- NH3 icy mixtures. We have completed low-temperature spectroscopic studies (1 to 20 microns) of H2O -rich ices containing NH3, with an emphasis on features in the near-IR region, which is accessible to ground-based observers. Conditions for the formation and thermal stability of the ammonia hemihydrate and the ammonia monohydrate have been examined. The former undergoes a slow loss of NH3 in a vacuum environment, to give the monohydrate. Additional warming removes the remaining NH3 to give the spectrum of H2O -ice. IR band positions of NH3 in different H2O -ices have been tabulated, and compared to the positions for NH3 hydrates over a large temperature range. We report spectral shifts that depend on both concentration and temperature. The radiation-induced amorphization of hydrates was observed and the radiolytic destruction of NH3 in H2O -ices was measured. We also have tabulated the near-IR spectral position of the ammonium ion which is observed to form in irradiated water and ammonia ices. Implications of these results for the formation, stability, and detection NH3 on Charon and other icy satellite surfaces will be discussed.
691.gsfc.nasa.gov/cosmic.ice.lab/

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