Water ice and radiation in the solar system
Infrared detection of water ice phase can reveal the temperature and radiation history of a surface. In this dissertation, I will describe and quantify the process of amorphization of crystalline ice through lab experiments and computer simulations. I will then show how these measurements can be applied to ground based observations.
The amorphous phase of solid water forms at temperatures less than 130 K, and converts to crystalline ice at 135 K in an exothermic and irreversible reaction. The amorphous and crystalline phases have distinctive spectra in the infrared. However, ion irradiation of crystalline water ice in the lab makes the infrared spectrum indistinguishable from that of amorphous ice. If the process of amorphization can be quantified, the model can be applied to various planetary surfaces, using an estimate of the temperature and the radiation environment.
This work sheds light on the physical processes behind amorphization. I will show that the irradiation of crystalline ice does not create the amorphous phase of ice, but produces a sample that is spectrally indistinguishable from amorphous water ice. The changes in the spectral features are caused by the breaking of OH and hydrogen bonds among other processes. The temperature dependence of this process is a function of the ability of free hydrogen and oxygen to reform the crystalline lattice.