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M. H. Moore (NASA/Goddard Space Flight Center), R. F. Ferrante, J. Stone (US Naval Academy), R. L. Hudson (Eckerd College)
Although water- and ammonia-ices have been observed or postulated as important components of the icy surfaces of planetary satellites in the outer solar system, significant gaps exist in our knowledge of the spectra and behavior of such mixtures under astrophysical conditions. In our laboratory we recently have undertaken low-temperature spectroscopic studies (1 to 20 microns) of water-ammonia mixtures, with special emphasis on features in the near-IR, a region which is accessible to ground-based observations. Our laboratory work was completed at NASA/Goddard's Cosmic Ice Laboratory where IR spectra of low-temperature ices can be studied as a function of MeV proton bombardment, which simulates accumulated cosmic-ray processing. The influences of composition, formation temperature, thermal- and radiation-processing, and phase (crystalline or amorphous) of the components were examined. Conditions for the formation and stability (both radiation and thermal) of two of the three stable ammonia hydrates (NH3:H2O = 2:1 and 1:1) have been completed. Work on the NH3:H2O = 1:2 hydrate is in progress. These results will be summarized in this presentation, along with similarities between the near-IR spectra of ammonia hydrates and the ammonium ion. Implications for the formation, stability, and detection of these ammonia species on outer satellite surfaces will be presented.
This work is supported by NASA's Planetary Atmospheres Program.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.