Io's hot spots in the near-infrared detected by LEISA during the New Horizons flyby

Abstract

The New Horizons spacecraft flew past Jupiter and its moons in February and March 2007. The flyby provided one of the most comprehensive inventories of Io's active plumes and hot spots yet taken, including the large 350 km high eruption of Tvashtar. Among the suite of instruments active during the flyby was the Linear Etalon Infrared Spectral Array (LEISA), a near-infrared imaging spectrometer covering the spectral range 1.25 to 2.5 μm. We have identified 37 distinct hot spots on Io in the nine LEISA spectral image cubes taken during the flyby. We describe the thermal emissions from these volcanoes and fit single-component blackbody curves to the hot spot spectra to derive eruption temperatures, areas, and power output for the hot spots with sufficient signal-to-noise. Of these, 11 hot spots were seen by LEISA more than once, and East Girru showed short-term variability over a few days, also seen by other New Horizons instruments. This work presents a comprehensive look at the global distribution of Io's volcanism at the time of the flyby. From these measurements, we estimate the global power output of high-temperature (>550 K) volcanism on Io to be ~8 TW. This work provides the first short-wavelength near-infrared survey with global coverage at all longitudes on the nightside of Io without sunlight contamination at these wavelengths. A major conclusion from this study is that 90% of all the volcanoes observed in the New Horizons LEISA near-infrared data in 2007 were also observed during the Galileo epoch, suggesting these are all long-lived hot spots.