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J. R. Spencer (Lowell Obs.), Io Community Panel 0
Io is a target of extreme scientific interest, due to its hyperactive geology, unique atmosphere, and unique role in the Jovian magnetosphere. Nowhere else beyond Earth can we watch large-scale geology in real time. Io is also important for what it tells us about other bodies. Its high heat flow provides a window into conditions on the early Earth at the time life began. An understanding of Io's tidal heating is important for understanding the coupled tidal heating that may support an ocean on Europa. Io's tidal heating and magnetospheric effects also provide analogs for processes that may occur in the satellite systems and magnetospheres of extra-solar giant planets.
Much remains to be learned. For instance we do not understand why Io emits more heat that can be generated by steady-state tidal heating. Galileo's brief snapshot observations have not shown us Io's full range of eruption styles. We do not know the composition of the erupted lavas, or understand how Io's volcanos supply gas and plasma to the atmosphere and Jovian magnetosphere. Io may be most feasibly studied by a long-duration mission in Jovicentric orbit, with continuous distant monitoring and frequent close Io approaches, possibly supplemented by penetrators. Such a mission is technically much easier than the proposed Europa orbiter and could also be broadened into a "Tidal Heating Explorer" investigating all the Galilean satellites. A modern spacecraft could vastly increase our understanding beyond that provided by Galileo's 1980-vintage instrumentation and very low data rate.
We propose that future missions to Io should include funds for ground-based support. Io's unpredictability means that high temporal and spatial resolution ground-based observations of Io will be an invaluable and cost-effective supplement to space missions, and are also important in their own right. Also, as Io's atmosphere and plumes are best studied in the UV, we urge development of a space-based UV telescope to replace and extend the capabilities of HST for Io and/or other planetary studies.
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