Thermal Mapping of Io using the Galileo Near Infrared Mapping Spectrometer

W.D. Smythe, R.M.C. Lopes-Gautier, A.G. Davies, R.W. Carlson (JPL-Caltech), L.A. Soderblom (USGS-Flagstaff), Galileo NIMS Team

A thermal map of Io has been developed using data from the Galileo Near Infrared Mapping Spectrometer (NIMS). The instrument has detected numerous and persistent hot spots on Io which are easily recognizable at the red end of the instrument's spectral range, 0.7-5.2 tex2html_wrap_inline11 m. These hot spots exhibit apparent color temperatures ranging from 400 to 600 K (single temperature fit) and appear to consist of small high temperature areas surrounded by "warm" regions. NIMS can detect temperatures down to 180 K for areas which fully fill the field of view, a minimum which rises for smaller areas. The effective spatial resolution for a thermal map can be much higher than the nominal instrument spatial resolution, because individual color temperatures are sampled 24 times in a sliding window across the instrument field of view.

It is most straightforward to use nightside observations rather than dayside observations of Io to develop a thermal map because of the complications involved in separating reflected and emitted radiation. Nightside observations were obtained in orbits G1, G2, E6, and G7. The thermal map can be used to compare the thermal output of the hot areas and the "warm" regions.