The crystalline state of water ice in the Solar System depends on thetemperature history of the ice and the influence of energetic particles towhich it has been exposed. We measured the infrared absorption spectra ofamorphous and crystalline water ice in the 10-50 K and 10-140 K temperaturerange, respectively, and conducted a systematic experimental study toinvestigate the amorphization of crystalline water ice via ionizing radiationirradiation at doses of up to 160 \pm 30 eV per molecule. We found thatcrystalline water ice can be converted only partially to amorphous ice byelectron irradiation. The experiments showed that a fraction of the 1.65 \mumband, which is characteristic for crystalline water ice, survived theirradiation, to a degree that strongly depends on the temperature. Quantitativekinetic fits of the temporal evolution of the 1.65 \mum band clearlydemonstrate that there is a balance between thermal recrystallization andirradiation-induced amorphization, with thermal recrystallizaton dominant athigher temperatures. Our experiments show the amorphization at 40K wasincomplete, in contradiction to Mastrapa and Brown's conclusion (Icarus 2006,183, 207.). At 50 K, the recrystallization due to thermal effects is strong,and most of the crystalline ice survived. Temperatures of most icy objects inthe Solar System, including Jovian satellites, Saturnian satellites (includingTitan), and Kuiper Belt Objects, are equal to or above 50 K; this explains whywater ice detected on those objects is mostly crystalline.
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