Future Io Exploration for 2013-2022 and Beyond: A White Paper submitted for the 2011 Planetary Science Decadal Survey

Jupiter's satellite Io is the most geologically dynamic solid body in the Solar System. Io undergoes severe tidal heating, induced by the orbital eccentricity forced by Jupiter and the 4:2:1 Laplace resonance between Io, Europa, and Ganymede. Io's high global heat flow (>2 W m-2, compared to the 0.06 W m-2 average for Earth) presages an extremely rich array of geophysical, geological, geochemical, and atmospheric phenomena operating at a scale not currently seen active anywhere else in our Solar System. Thus we are not restricted, as on other planetary bodies, to reconstructing processes from their long-dead remains. Io also is the main source of neutral gas, plasma, and dust to the Jovian magnetosphere. And importantly, Io is the best place in the Solar System to study the effects of tidal heating. Testing models of tidal heating on Io has implications for many satellites in our own Solar System, and to the possibility of expanded habitability zones in extrasolar systems. Io's history is directly linked to the evolution of the one of most promising sites for extraterrestrial life, Europa. By studying the time-variable orbital and thermal evolution of Io, we also gain a better understanding of time-variable tidal heating of Europa, with obvious implications for the sustainability of its putative subsurface ocean and history of habitability. An Io-dedicated mission that operates in the 2013-2022 timeframe could identify key parameters involved in Europa’s orbital-thermal evolution, which can be further investigated by the NASA-ESA Europa-Jupiter System Mission's (EJSM) orbiters when they enter the Jovian system in 2025. This presentation will review the science objectives and proposed mission concepts for future exploration of Io in the next decade and beyond. We recommend specific mission concepts and instruments be implemented during the next Decadal Survey period. These include: 1) a Jupiter-orbiting spacecraft (Io Observer) of either Discovery-class or New Frontiers-class designed to investigate the tidal heating of Io and its effects; 2) a space-based UV telescope with diffraction-limited capability, that is able to resolve Io; 3) monitoring of Io's volcanism over a variety of time scales (seconds, minutes, hours, days, months, years) and spectral and spatial resolutions on future Jovian missions, as is currently planned by EJSM; and 4) expanded time for infrared Io observations by ground-based 8- to 10-m class telescopes, particularly those with Adaptive Optics capability.