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]

Io Talks at DPS 2009

The science program as well as the abstracts for this year's DPS meeting were posted online a few weeks ago. DPS 2009 will be taking place in Fajardo, Puerto Rico, and as such, I won't be going. Hopefully the organizers will be able to broadcast the meeting oral sessions like they did for last year's meeting, but I guess that will depend on the infrastructure at the El Conquistador Resort. The webcasts last year allowed me to post about each of the Io talks here on this blog.

The 2009 Meeting of the Division of Planetary Sciences will be held between October 4 and 9, 2009.

In this year's science program, there are four Io talks and one poster planned. All four Io talks will be held during the Galilean Satellites oral session on the afternoon of Friday, October 9. The Io-related poster will be in the Decadal Survey White Papers section during the poster session on the evening of Tuesday, October 6. Here is a brief summary of the talks and posters to be presented:

• The first talk of the Galilean Satellites session is titled, "Strong Tidal Dissipation In Io And Jupiter From Astrometric Observations" and is by Valery Lainey et al. The talk will summarize their results from examining astrometric data of the Galilean satellites over the last century and what the motions of these moons tell us about the rate of tidal dissipation within Io. They found that the dissipation rate is on the same order as Io heat flow, suggesting that Io is in thermal equilibrium. These results were published in a paper in the journal Nature earlier this year and were discussed in more detail on this blog then.
• The next talk will be by Daniel Allen and Jani Radebaugh and is titled, "Temperature and Variability of Three Ionian Volcanoes." The authors examined the brightness and color temperature of three volcanoes on Io (Pillan, Wayland, and Loki), observed by Cassini's narrow-angle camera during several eclipses during the New Year's 2001 Cassini encounter. The abstract and talk provide an update to the results presented at this year's Lunar and Planetary Sciences Conference back in March, including updated temperature estimates for the three volcanoes. They found a cooling trend for Pillan and Wayland, suggestive of a cooling lava flow, as well as an apparent shut down of a vent at Wayland during one of the eclipses. Loki was found to be more variable, consistent with an active lava lake.
• John Spencer et al. will present the next talk in the Galilean satellites session, titled, "Changes in Io's Atmosphere in 2009: Atmospheric Inflation Near Perihelion?". During his talk, Spencer will present spectroscopic observations of Io's atmosphere acquired in June 2009 which suggests that Io's atmosphere undergoes an increase in column density (the amount of gas over a given area on Io's surface) as the Jupiter system approaches perihelion. This would be the result of increased sublimation of sulfur dioxide frost from Io's surface from the increased surface temperatures. The vapor-pressure equilibrium relationship between SO2 surface frost and atmosphere SO2 gas is sensitive enough that even the 5.6 K temperature difference between aphelion and perihelion is expected to produce a 7x difference in atmospheric SO2 vapor pressure. This data was also discussed in more detail by John Spencer in June in the Planetary Society Blog.
• The final Io talk in the Galilean satellites session will be presented by Jessica Lovering and is titled, "Analysis of the New Sodium Emission Feature Discovered in Io’s Wake". The discovery of this Jupiter-ward sodium jet was presented at last year's DPS and was discussed to an extent on this blog then.
• The Io poster covers the Io Decadal Survey White Paper and will be presented by David Williams. The two white papers were discussed on this blog earlier.

EDIT 09/19/2009 4:17 pm: Fixed links to abstracts...hopefully...  If you are having trouble with the links, just go to the two sessions with Io talks and posters and click the links their for the abstracts: Galilean satellites oral session and Decadal Survey White Papers poster session.

Link: DPS 2009 Meeting [dps09.naic.edu]

Io Decadal Survey White Paper

The Planetary Science Decadal Survey is now well underway as the community discusses how NASA should spend its money in the discipline over the decade from 2013 to 2023. For the outer planets, the previous decadal survey made a Pluto flyby mission and a Jupiter atmospheric orbiter two of its main priorities. These mandates later morphed into the New Horizons and Juno missions. At this point in the process this go around, various groups in the community are producing white papers, documents that provide details as to what should be the priorities over the next decade for their subject, be it technology, planetary astronomy, Titan, Europa, or Io, for example. NASA's Outer Planets Assessment Group (OPAG) website has several drafts for some of these white papers, including the latest draft of the Io white paper. Additional submitted white papers can be found on the decadal survey website (check out some of the ones at the bottom of that page for a laugh).

The Io white paper being authored by Dave Williams from ASU with many others, including myself, in the Io community providing input. The paper is split up into two parts: Part 1 discusses why exploring Io should be important to the rest of the community and what kinds of science goals are needed for a future mission to the satellite; Part 2 explores the types of missions that should be sent to Io in the next decade and beyond.

While the first part of the white paper roughly follows the document from the previous decadal survey, explaining why exploration of Io is important, the second parts provides updates for recommendations to the NASA Space Science Division for future Io exploration:

1. A balanced program between life-focused and general exploration missions
2. A more modest (compared to EJSM) 'Io Observer' Discover- or New Frontiers-class mission
3. The support of the IVO mission, currently being studied for the next Discovery AO
4. New Frontiers-class mission concepts for the next New Frontiers AO that allows radioisotope power sources
5. An Io orbiter in the 2023-2033 timeframe to follow-up on the discoveries of a Jupiter-orbiting 'Io Observer'
6. Io in-situ missions in the same timeframe, including penetrators, landers, and rovers that would help constrain the size and physical state of Io's core and better understand Io's surface and lower atmospheric chemistry
7. A space-based ultraviolet telescope to replace Hubble with diffraction-limited capability in the next decade
8. Long-lived Jupiter missions that would provide opportunities to observe Io over long-time frames (Juno and EJSM may provide these types of observations over the next two decades)
9. Expanding the time available for planetary astronomy on 10-meter class telescopes with Adaptive Optics capability. Such time availability would allow for long-term studies of Io's volcanic activity even without a spacecraft in the Jupiter system
10. Including support for ground-based observation programs with Jupiter system missions to follow-up on discoveries of volcanic eruptions

These recommendations highlight the need to study Io's time-variable phenomena and to close the gaps in temporal coverage of Io's volcanic activity, whether it be using Jupiter-system missions (dedicated to Io or not) or Earth-based telescopes.

Link: Planetary Science Decadal Survey White Papers [www8.nationalacademies.org]