Subject: Outstanding Questions About the Galilean Satellites for Final Discussion

"What five issues are the most significant in furthering our understanding of the nature and evolution of the Galilean satellites?" Here is the final set of questions from each individual. I have also reordered the questions in a thematic format so that we can discuss them in a coherent manner. Following our completion of the reading topics tomorrow, I would like to begin discussion more or less in the order indicated on the thematic list, and I would like each individual to contribute to the discussion with some short explanation of their logic or how to address the question now or with future measurements and exploration.

Marty Gilmore:

  1. What is the nature of the crust of Io, specifically what is the proportion of silicates in the crust?
  2. Is Europa presently or recently active? Is there a liquid water ocean beneath the crust?
  3. What is the genesis of curvilinear ridges on Europa?
  4. We still do not know the impact flux at the orbit of these satellites to perform crater age dating.
  5. Is the dark terrain on Ganymede equivalent in age to the surface of Callisto, or, what are the processes and time scales involved in darkening of ice?

Irene Antonenko:

  1. What is the composition of high topography areas on Io?
  2. How do triple bands form on Io? Dark versus light material composition, age?
  3. Is Europa currently volcanically active/capable of being active?
  4. What is the rheology of planetary ices past and present? Are early craters viscously relaxed into obscurity.
  5. What are the stratigraphic relationships between dark and bright terrain on Ganymede?

Louise Prockter:

  1. Nature of surface stresses past and present.
  2. Rheology of ice; implications for viscous relaxation, resurfacing and tectonics.
  3. Nature of volatiles; composition and areal abundance.
  4. Nature and age of resurfacing materials and mode of emplacement.
  5. Existence of a liquid water ocean on Europa.

Cathy Weitz:

  1. Satellite structure: What is the internal structure of the Galilean satellites (i.e, differentiated, core, etc)?
  2. Tectonics: How and when did the silicate mountains on Io form? What is the cause of the grooved terrain on Ganymede? How did the triple bands and arcuate bands form on Europa?
  3. Surface Processes: How do the icy surfaces weather through time and how does this affect their albedo?
  4. Volcanism: What is the role of sulfur and silicates in ionian eruptions? Has explosive water volcanism occurred on any of the other satellites?
  5. Cratering: How did the palimpsests and their ring systems form on Callisto and Ganymede?

Steve Herzog:

  1. What is the composition of Ganymede's ancient dark terrain and is it the same as the dark terrain which covers Callisto? What are the satellite's bulk compositions?
  2. Why has Ganymede's ancient dark terrain broken up into discrete pieces (cf. Callisto)?
  3. How does the breakup of Ganymede dark terrain and emplacement of bright grooved terrain occur?
  4. What is the process responsible for the formation of triple bands on Europa?
  5. Why is the apparently older surface material on Europa lighter and why is it so light? Is it water frost? If so, how is it being emplaced.

Li Lin:

  1. What are important factors controlling the evolution of Ganymede and Callisto? How did these factors result in the apparent contrast between their surface features?
  2. Is the formation of grooved terrain due to the global expansion of Ganymede or other origin?
  3. How did the mixture of ice-rock influence on the morphology of craters on ice satellite? Did water-ice also control the crater morphology in same way as on Mars?
  4. Is there a water mantle between Europa's crust and core? If so, why aren't there the formation of grooved terrain like on Ganymede?
  5. Are there the original relationship among grey bands, triple bands and wedge-shaped bands on Europa?

R. Aileen Yingst:

  1. What is the level of differentiation of each Galilean satellite?
  2. What is the thermal and chemical behavbiour of water ice polymorphs?
  3. What are the internal compositions of the Galilean satellites, and how do they differ from one another, and form their surface compositions?
  4. What is the impact history of the Jovian system?
  5. What is the thermal budget of each moon, and what determined its thermal history?

Geoff Collins:

  1. Are the tectonic features on the satellites dominantly controlled by global stresses (despinning, volume change, tidal stresses) or by local stresses (plumes, convection, plate motion)?
  2. How do the dark terrain on Ganymede and Callisto and the dark lineaments on Europa form? What is the composition of this material and, if it is denser, how can it rise through or be stable upon an icy mantle?
  3. What is the composition and rheology of the ices on the surfaces of these satellites? Will it allow viscous relaxation and over what timescale? How old is the oldest surface on these satellites? Is it equivalent in age to the lunar highlands?
  4. Why is the flux of impactors in this system? How can we find the absolute age of any surface?
  5. Is there any liquid water ocean under Europa's icy shell? Can it harbor life?

Bob Pappalardo:

  1. What is the timing of endogenic activity on each of the satellites? Is early activity related to differentiation?
  2. What is and has been the nature, composition, and structure of each satellite's crust, lithosphere, and asthenosphere?
  3. What is the range of the volcanic styles on each satellite? What are the relative roles of silicates, water ice, and volatiles?
  4. What internal processes have operated to create and influence the surface expressions of Ganymede's and Europa's tectonic structures?
  5. Does Europa presently have a subsurface ocean or did it have one in the past? If it presently has an ocean, can it sustain microbial life?

Thematic and Process Questions: