Detailed Studies of Amorphous and Crystalline Ice in the Solar System
Water ice spectra have been obtained from many outer solar system objects, where they have proved useful in determining surface properties such as temperatures, grain sizes, and the presence of trace contaminants. In some cases, the presence of amorphous vs. crystalline ice has been used to interpret the recent thermal and radiation history of the surface [Hansen and McCord 2004]. This study carefully quantifies the conditions under which amorphous and crystalline ices are formed and applies that knowledge to icy objects in the outer solar system.
The tasks covered in this study consist of (a) acquiring near-IR spectra of Galilean, Saturnian and Uranian satellites, including Galileo/NIMS and Cassini/VIMS spectra, (b) modeling the surface environments (temperature and UV/charged particle fluxes) associated with local spectra observations, and (c) developing rules based on these real-life laboratories for the amorphization and crystallization rates of H2O-ice. The presence of amorphous ice on the warm surfaces of Europa and Ganymede is currently an unexplained problem, as is the near-ubiquitous presence of crystalline ice on the surfaces of Charon, several Kuiper belt objects, and the large Uranian satellites. If the rates of amorphization and crystallization were understood in the context of relevant solar system environments, then the observed state of H2O-ice on remote objects might serve as useful constraints on the recent history of those objects.