Final Version of the Io Decadal Survey White Paper Posted

The final draft of the Io Decadal Survey White Paper has been posted online.  The white paper consists of two sections: the first summarizes the state of Io science, the justification for NASA sending additional missions, and the outstanding questions that should be addressed by future exploration of the satellite; the second discusses an exploration strategy for addressing these remaining questions.  The other submitted white papers can be found on the National Academies website; Van Kane has a good summary on his blog of these other papers.  I previously posted a note about the recommendations for future missions to Io based on an earlier draft of the white paper.

Let's take a look at the two Io white papers.  The first, Justification and Science Objectives, takes a look at the reasons why other planetary scientists should be interested in exploring Io, the outstanding questions left by the exploration of Io by Galileo and New Horizons, and the science objectives that a future Io mission or series of Io missions should attempt to accomplish.  In addition to the fact that Io is just plain awesome and everyone knows it ("Finally, as one of the most spectacular places in the Solar System, Io has unique public
appeal, and Io exploration offers many opportunities to attract and engage public interest in
planetary science."), the authors point out that studying Io provides opportunities to understand processes that are important to examine in general, including: satellite-magnetosphere interactions; the mechanics of tidal heating, an important process for Io as well as Europa, Ganymede, and Enceladus, as well as for extra-solar planetary systems; volcanism, particularly that found on the Moon and Archean Eon Earth; and the dynamics of thin atmospheres, particularly those which are strongly driven by surface temperature and vapor pressure. The authors also identified eight science objectives that an Io exploration campaign would attempt to accomplish (the sub-headings are my own notes):

1. Determine the magnitude, spatial distribution, temporal variability, and dissipation
   mechanisms of Io’s tidal heating. (We would like to add “and implications for the coupled
   orbital-thermal evolution of Io and Europa.”)
1. The latter goal can be helped by the examination of Europa to be performed by EJSM.
   
2. Determine Io’s interior structure, e.g., whether it has a magma ocean.
3. Determine whether Io has a magnetic field.
1. This fits into the previous objective.  As explained later in Part 1, understanding the state of the core, its Fe/S ratio, and its size would help us understand the result obtained by Galileo that suggests that Io does not have a magnetic field.  Resolving the conundrum of why Io can be so active and not have one might help us better understand how planetary magnetosphere are created.
4. 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.
1. Two good places to provide comparative studies would be the Moon and Mercury.  While these two worlds are dead as a doornail now (deader actually), earlier in their histories, they experienced volcanic eruptions similar to those we see on Io now, particularly flood basalt eruptions and pyroclastic flows.
5. 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 planets.
1. In addition to the high-resolution observations to be obtained by Io-centric missions discussed in Part 2 of the white paper, additional information could be gained for this goal from the Ice-Penetrating Radar (IPR) on board the Jupiter Europa Orbiter during its two of its close flybys.
6. Understand Io’s surface chemistry, including volatiles and silicates, 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.
7. 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 volcanism.
8. Investigate the neutral and plasma densities and energy flows in the Io plasma torus, plus their
   variations over time, and characterize the ionic radiation belts in the vicinity of Io and their
   influence on the surface.
   

The second part of the Io white paper, Recommendation for Missions, was more extensively discussed in my last post on this subject.  To answer Ted's comment for that post, where he suggested that IVO, a proposed Discovery-class Io mission, would be the most likely to fly, keep in mind that what is discussed in Part 2 is an exploration program, akin to what is currently going on for Mars.  For Io, this program would start with either a New Frontiers- or Discovery-class mission that would orbit Jupiter and flyby Io on several occasions.  Such a mission could be flown in the 2013-2023 decade covered by this survey.  Following this "Io Observer" mission, the next decade, 2023-2033, could see a follow-on mission that would orbit Io, providing detailed global maps using UV, visible, and near-infrared imagers and a laser altimeter, as well as measuring Io's gravity and possible magnetic fields, and deploy one or more in situ components, such as penetrators, landers, or rovers.  One important task for these in situ missions would be to measure seismic activity using seismometers.  Enough activity should be detected over a period as short as a day to provide a more detailed model of Io's interior structure.  Finally, the authors support telescopic observations of Io from Earth or from space-based platforms, including a UV telescope that would replace the capabilities that will be lost once Hubble is de-orbited and additional ground-based telescopes with adaptive optics capabilities, which would help ease scheduling pressures at telescopes such as Keck II.  These observations would allow for monitoring time-variable phenomenon at Io such as satellite-magnetosphere interactions, Io's atmosphere, and its volcanic activity.

Additional white papers can be found at the National Academies website as well as summaries at Van Kane's blog.  These white papers will be used as input into the upcoming Decadal Survey report, which will outline the direction planetary science should go within NASA over the next decade.  How much will be possible is up in the air as the planetary budget is projected to remain pretty flat over the next decade.  For Io, since the recommendations call for a fairly modest program over the next decade (one mission in either the New Frontiers or Discovery programs) with the major mission to be started in the decade following, it isn't impossible that such a program could fly.  What remains to be seen is how much NASA and the community will take to heart the first suggestion made by the authors of the Io white paper:

We recommend that NASA pursue a balanced solar system exploration program between life-focused and physical-science focused missions.

Link: Future Io Exploration for 2013-2022 and Beyond, Part 1: Justification and Science Objectives and Future Io Exploration for 2013-2022 and Beyond, Part 2: Recommendations for Missions [www8.nationalacademies.org]