Near Infrared Spectral Radiance at Multiple Wavelengths From Io's Volcanoes 1: The Low Spatial Resolution Night-Time Galileo NIMS Data Set

We have calculated surface-leaving spectral radiances for 285 detections of volcanic thermal emission from Io observations made by the Galileo Near Infrared Mapping Spectrometer (NIMS) in the 0.7- -5.2-mu m wavelength range, the first such analysis of the entire low-spatial-resolution night-time data set. Most of these detections are of 53 individual hot-spots. We establish that 4.8-mu m spectral radiance is a good proxy for total thermal emission from a hot spot. Many detections reported here have not been previously modeled. This set of hot-spot detections is derived from NIMS night-time observations obtained between June 1996 (orbit G1) and October 2001 (Orbit I32), where the hot-spot is sub-pixel. Modeling of the spectra yields total thermal emission from each volcano in each observation, as well as the 2:5-mu m spectral radiance ratio and radiant flux density. Surface-leaving spectral radiance is derived at 2.0, 3.5, 3.8, 4.8, and 5.0 mu m allowing direct comparison with data obtained by other spacecraft and ground-based telescope data. The most energetic volcanic eruptions are identified. We find an unusual number of sources in a C30 observation suggesting that a vigorous volcanic activity was taking place simultaneously in multiple locations, possibly tidally controlled.