THE IO VOLCANO OBSERVER (IVO): A NASA DISCOVERY MISSION CONCEPT TO INVESTIGATE TIDAL HEATING

Io is the most tidally heated body in the Solar System, leading to the development of hundreds of active volcanoes on its surface. This makes Io an exciting target for future exploration and the Io Volcano Observer (IVO) is uniquely capable of providing essential observations to test hypotheses about how Io generates, transports, and loses heat. The processes involved are fundamental to the thermal evolution of all planetary bodies and are especially relevant to the early Earth–Moon system as well as tidally-heated ocean worlds like Europa, Ganymede, Titan, and Enceladus. One of the major outstanding issues relating to Io—and tidal heating in general—involves how and where tidal energy is dissipated. In one scenario, Io’s mantle has a low melt fraction, leading to solid-body dissipation in the deep-mantle or asthenosphere. In an alternative scenario, Io’s interior includes a high proportion of silicate melt, leading to the formation of a globally continuous partial melt layer, or subsurface “magma ocean”. If a magma ocean exists within Io, fluid-body dissipation could play a dominant role in heating Io’s interior, with resonances having a tremendous effect in determining the efficiency of tidal dissipation. By virtue of the Laplace resonance, tidal dissipation within Io is intimately linked to the thermal history of the other Galilean satellites. Io is therefore an exceptional target for future exploration and IVO is ideally suited to distinguish between interior models by measuring its: (1) global distribution of volcanism and tectonism; (2) mantle electrical conductivity profile: (3) tidal Love number and phase lag; and (4) libration. IVO will accomplish this with measurements by re-flights of the Europa Clipper’s Europa Imaging System and Plasma Instrument for Magnetic Sounding, a thermal mapper, pair of magnetometers, and a mass spectrometer. Together these observations will lead to revolutionary advances in understanding the thermal evolution Io and other tidally-heated worlds.