Ammonia–water ice laboratory studies relevant to outer Solar System surfaces

• Published in: Icarus (New York, N.Y. 1962) Vol. 190; no. 1; pp. 260 - 273
• Main Authors: Moore, M.H., Ferrante, R.F., Hudson, R.L., Stone, J.N.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01-09-2007; Elsevier
• Subjects: Astronomy; Charon; Earth, ocean, space; Exact sciences and technology; Ices; Satellites; Solar system; Spectroscopy; surfaces; Trans-neptunian objects; Spectroscopy; Charon; Satellites; Ices; Trans-neptunian objects; Laboratory study; surfaces; Spectroscopy; Ice; Spectral line shift; Thermal stability; Ammonia; Thermal radiation; Pluto satellite; Radiation temperature; Natural satellites; Positions; Solar system; Ices; Charon; Trans-neptunian objects; Satellites; Planetary surfaces; Low temperature
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2007.02.020

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. To that end, we have completed low-temperature spectroscopic studies (1–20 μm) of water–ammonia mixtures, with an emphasis on features in the near-IR, a region which is accessible to ground-based observations. The influences of composition, formation temperature, thermal- and radiation-processing, and phase (crystalline or amorphous) of the components were examined. Spectra of both pure NH
3 and H
2O–NH
3 icy mixtures with ratios from 0.7 to 57 were measured at temperatures from 10 to 120 K. Conditions for the formation and thermal stability of the ammonia hemihydrate (2NH
3⋅H
2O) and the ammonia monohydrate (NH
3⋅H
2O) have been examined. Band positions of NH
3 in different H
2O-ices and major band positions of the hydrates were measured. We report spectral shifts that depend on concentration and temperature. The radiation-induced amorphization of the hemihydrate was observed and the radiation destruction of NH
3 in H
2O-ices was measured. Implications of these results for the formation, stability, and detection of ammonia on outer satellite surfaces are discussed.