Abstract
During the Cassini-Jupiter flyby, VIMS observed Io at different phase
angles, both in full sunlight and in eclipse. By using the sunlight
measurements, we were able to produce phase curves in the visual
through all the near infrared wavelengths covered by the VIMS instrument
(0.85-5.1 mum). The phase angle spanned from similar to2degrees to
similar to120degrees. The measurements, done just after To emerged
from Jupiter's shadow, show an increase of about 15% in Io's reflectance
with respect to what would be predicted by the phase curve. This
behavior is observed at wavelengths > 1.2 mum. Moreover, just after
emergence from eclipse an increase of about 25% is observed in the
depth of SO2 frost bands at 4.07 and 4.35 mum. At 0.879 < lambda
< 1.04 mum the brightening is 10-24%. Below lambda = 0.879 mum the
brightening, if present, should be less than the precision of our
measurements (similar to5%). Apparently, these observations are not
explained neither by a diverse spatial distribution of SO2 on the
Io' surface nor by atmospheric SO2 condensation on the surface during
the eclipse. (C) 2004 Elsevier Inc. All rights reserved.
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