Vision and Voyages for Planetary Science in the - Solar System ...

FIGURE 8.1 Montage of the major outer planet satellites, with Earth’s Moon for scale. Ganymede’s
diameter is 5262 km. The Moon’s diameter is 3476 km. SOURCE: NASA.
All three of the crosscutting science themes for the exploration of the solar system motivate
further exploration of the outer planet satellites; their study is vital to addressing many of the priority
questions in each of the themes. For example, in the Building New Worlds theme, the satellites retain
chemical and geological records of the processes of formation and evolution in the outer solar system—
records no longer accessible in the giant planets themselves. As such the satellites are key to attacking the
question “how did the giant planets and their satellite systems accrete, and is there evidence that they
migrated to new orbital positions?” The Planetary Habitats theme includes the question “what were the
primordial sources of organic matter, and where does organic synthesis continue today?” The surfaces
and interiors of the icy satellites display a rich variety of organic molecules—some believed to be
primordial, some likely being generated even today; Titan presents perhaps the richest planetary
laboratory for studying organic synthesis ongoing on a global scale. Europa, Enceladus, and Titan are
central to another key question in this theme: “beyond Earth, are there modern habitats elsewhere in the
solar system with necessary conditions, organic matter, water, energy, and nutrients to sustain life, and do
PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION
8-3