NEW HORIZONS IMAGES OF IO VOLCANISM REVISITED: A JUNO PRELUDE

New Horizons flew through the Jupiter system on February 28th 2007, on its way to Pluto. During the flyby its cameras obtained 177 high-resolution panchromatic images of Io, with pixel scales as small as 11.2 km, and about a dozen lower-resolution color images, at a wide range of viewing and illumination geometries. The result was the best imaging data set for Io between Galileo and the imminent Juno close flybys. Major results from these data have been published (e.g. Spencer et al. 2007, Rathbun et al. 2014, Hoey et al. 2021), most notably extensive data on a major plume and hot spot eruption at Tvashtar. However, the images contain a wealth of additional information on Io's plumes and surface that has not been fully exploited, and is worthy of a second look. Image quality can be significantly improved by processing techniques developed for the Pluto encounter.

New results include some surprising plume phenomena, and new details on the remarkable photometric behavior of Io’s surface, in both sunlight and Jupiter shine, including quasi-specular scattering from some terrains seen at high phase angles. Color imaging in sunlight, and at night in Jupiter-shine, also provides unique temporal coverage of Io’s short-lived sulfur-rich red plume deposits.