Program: GN-2016A-Q-33

The most volcanically active body in our Solar System, Jupiter's moon Io presents a unique analog for volcanism in the early Solar System, and template for volcanically-active exoplanets. However, many fundamental questions surrounding Io's volcanism remained unanswered. Does Io erupt basaltic magmas such as we see on Earth today, or magmas of an exotic ultramafic composition such as were widespread in Earth's early history? What role does volcanic outgassing play in sustaining Io's sulfur-based atmosphere? We propose to address these two questions by using a rare opportunity when Io is in eclipse by Jupiter with another satellite near enough to use for wavefront sensing, to image Io during and after the eclipse (3 hours) with ALTAIR/NIRI at Gemini N from 1-4 microns. Observations down to 1 micron are required to measure the highest-temperature erupting component, which constrains magma composition, but such measurements must be made when Io is in shadow so that the reflected sunlight from the frost-covered surface doesn't overwhelm the thermal emission. The question of Io's atmospheric support will be addressed in conjunction with simultaneous (proposed) observations of volcanically-excited SO gas emissions at both Keck telescopes. The proposed Gemini N observations will allow us to link sites of greater SO emission with specific active regions on Io's surface.