Crystallinity and temperature of icy grains in comet C/2002 T7 (LINEAR) Original Research Article

We discuss the crystallinity and the temperature of water ice grains in the coma of comet C/2002 T7 (LINEAR) at 3.5 AU from the Sun. The observed relative reflectance spectrum in J and H bands can be reproduced by using the Hapke’s model. Due to limited S/N ratios of the observed spectrum, however, we can not identify the phase (crystalline or amorphous states) of water ice. Both crystalline and amorphous water ices can explain the observed spectrum within the errors. If the water ice was in amorphous state, the cometary ices formed and/or condensed in the molecular cloud or in the solar nebula (at further than 25 AU from the Sun). In contrast, if the cometary water ice was in crystalline state, the temperature of the icy grains in the coma could be estimated to be about 140–170 K, which is consistent with the temperature of sublimating dirty water ice grains at 3.5 AU.