Monday, December 15, 2008

Io Missions - Part Two: Science Goals

As discussed in previous posts, NASA is soliciting mission proposals for its next New Frontiers ($650M) planetary mission. Among the missions under consideration is an Io Observer. Government solicitations of proposals follow specific processes to ensure fairness to the proposers and to ensure that the government receives proposals relevant to its goals. NASA has published a 122 page preliminary Announcement of Opportunity (AO) for the New Frontiers solicitation. Among many other topics it lists the science goals for each possible mission. Since a great deal of thought goes into these AOs, this document is the best summary of the planetary science community's goals for each mission. For your convenience, I've copied the section on goals for an Io observer here (if you want to read them in the original AO, they start on page 8) as a succinct statement of science priorities for future Io missions.

Io Observer
Tidal heating, a process that can greatly expand the habitable zones in the solar system and elsewhere, is best studied at Io because it provides the most extreme example of this process in the solar system. Io provides the best place in the solar system, beyond Earth, to study volcanism, a process of fundamental importance on many planetary bodies. Io also provides some of the most dramatic, freshest, and easily-studied examples of fundamental geological processes such as mountain-building and mass wasting. The volcanic activity on Io drives interlocking processes on a variety of time scales. While resurfacing/recycling the surface, the activity also provides volatile contributions to the Jovian sulfur and sodium nebulae via a time-varying atmosphere and exosphere. By providing approximately 1 ton per second of material deep within the magnetosphere of Jupiter, Io is a primary driver for most magnetospheric activity. With transport of material to Europa and the rest of the system, reenergization processes, and the Alfvénic interaction between Io and the upper atmosphere of Jupiter itself, scientists know that multiple, nonlinear feedback processes are present on many spatial and temporal scales.

An Io Observer mission should address some of the following science objectives, which are not listed in order of priority:

• Determine the magnitude, spatial distribution, temporal variability, and dissipation mechanisms of Io’s tidal heating;
• Determine Io’s interior structure, e.g., does it have a magma ocean;
• Determine whether Io has a magnetic field;
• Understand the eruption mechanisms for Io’s lavas and plumes and their implications for volcanic processes on Earth, especially early in Earth’s history when its heat flow
was similar to Io’s, and elsewhere in the solar system;
• Investigate the processes that form Io’s mountains and the implications for tectonics under high-heat-flow conditions that may have existed early in the history of other
• Understand Io’s surface chemistry, volatile and silicate, and derive magma compositions (and ranges thereof), crustal and mantle compositions and implications
for the extent of differentiation, and contributions to the atmosphere, magnetosphere, and torus; and
• Understand the composition, structure, and thermal structure of Io’s atmosphere and ionosphere, the dominant mechanisms of mass loss, and the connection to Io’s

It is likely that there are more objectives here than can be included in a single New Frontiers mission; proposals must state the science goals for the proposed investigation
and provide a rationale for the choice of science objectives. Any mission architecture that achieves the majority of the science objectives stated above for Frontiers cost cap will be considered responsive to this AO.

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