Because the Ganymede Observer was not described in significant detail in the decadal survey, the committee chose to list science questions that such a mission could address, but stresses that this list should not be regarded as exclusive, and other science questions can also be considered for Ganymede. In no case should these science objectives be considered to be mission requirements; they are merely options.

  • Understand Ganymede’s intrinsic and induced magnetic fields and how they are generated, and characterize their interaction with Jupiter’s magnetic field.

  • Determine Ganymede’s internal structure, especially the depths to, and the sizes or thicknesses of, the probable metallic core and deep liquid water ocean, and the implications for current and past tidal heating and the evolution of the Galilean satellite system as well as ocean chemistry.

  • Understand Ganymede’s endogenic geologic processes, e.g., the extent and role(s) of cryovolcanism, the driving mechanism for the formation of the younger, grooved terrain, and the extent to which Ganymede’s tectonic processes are analogs for tectonics on other planetary bodies (both icy and silicate).

  • Document the non-ice materials on Ganymede’s surface, and characterize in detail the connection between Ganymede’s magnetosphere and aspects of its surface composition (e.g., polar caps).

  • Document the composition and structure of the atmosphere, identifying the sources and sinks of the atmospheric components and the extent of variability (spatial and/or temporal).


Scientific understanding of the solar system has continued to advance since the decadal survey was produced; thus, there may be new science to be explored that was not included in the decadal survey but might be viable as the basis for a New Frontiers mission. The committee concluded that NASA’s next New Frontiers announcement of opportunity should not be strictly limited to the eight mission options discussed above, but should also be open to proposals with extraordinary justification and inventiveness. This conclusion was the foundation for the committee’s third recommendation (see in Chapter 2 the section titled “Innovative Mission Options”).

The committee stresses, however, its third recommendation’s emphasis that any such mission option should “offer the potential to dramatically advance fundamental scientific goals of the decadal survey, and should accomplish scientific investigations well beyond the scope of the smaller Discovery Program.”


As the committee affirms at the beginning of this report, the New Frontiers Program is valuable and is a vital part of NASA’s solar system exploration program. It combines the strengths of both flagship and Discovery-class missions—the strategic emphasis in the flagship missions, which take their direction from the decadal survey, with the competition and innovation fostered by the Discovery missions. The committee’s ultimate goal is to provide NASA with sufficient options, and also to provide potential proposers with sufficient flexibility in their proposals, to enable NASA to select a mission that can be done within the constraints of the New Frontiers Program, particularly the cost cap.

The committee believes that as long as NASA provides the scientific community with the flexibility it requires, the next round of New Frontiers competition can produce the world-class science that has so far typified this program.

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