GALILEO SEARCH FOR SO2-FROST CONDENSATION ON IOS NIGHTSIDE

New, high-quality Galileo images of Io's dayside and Jupiterlit nights ide, examined for diurnal changes in violet albedo patterns and diurna l changes in hemispheric color, do not provide any evidence for signif icant nighttime condensation of the satellite's thin SO2 atmosphere. I n particular, the Galileo images do not show the major change in Io's average hemispheric color between day and night that was reported by B uratti et al. (1995, Icarus 118, 418-422) in a study of Voyager data. The lack of detectable nighttime frost deposition in the Galileo image s is not surprising, given the tenuous, ''patchy'' nature of Io's SO2 atmosphere and the associated difficulty in producing optically thick nighttime frost layers. (C) 1998 Academic Press.