Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p53b..03c&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P53B-03
Mathematics
Logic
[6218] Planetary Sciences: Solar System Objects / Jovian Satellites, [6222] Planetary Sciences: Solar System Objects / Ganymede
Scientific paper
Ganymede is unique in that it is the largest satellite in the solar system, the most centrally condensed solid body in the solar system, and the only solid body in the outer solar system known to posses an internally generated magnetic field. At the same time, its surface displays an array of geologic features spanning a wide range of ages and heat flow regimes, which serve as a reference point for understanding features on many other icy satellites. Ganymede’s geological history records evidence of the internal evolution of a large icy satellite, dynamical interactions with the other Galilean satellites, and the evolution of the population of small bodies impacting the surfaces of the satellites. Understanding Ganymede’s structure and history is an important key to understanding the Jupiter system, and large satellite systems around giant planets in general. Summarized here are some of the important questions we currently have about Ganymede: 1) Ganymede is highly differentiated, while its close sibling Callisto is not. What triggered differentiation? Did Ganymede differentiate near the time of accretion, or later in solar system history? 2) Modeling of Ganymede’s gravity field indicates there may be several near-surface mass anomalies. What causes gravity anomalies on icy satellites? What is the link with topography? 3) Two thirds of Ganymede’s surface is covered by bright grooved terrain, recording an episode of intense geological activity. Since the formation of grooved terrain, it appears that heat flow has decreased over time. Did Ganymede experience a pulse of tidal heating that triggered grooved terrain formation? Is it related to interior differentiation? Is it a record of Ganymede’s capture into the Laplace resonance with Europa and Io? 4) Ganymede’s internally generated magnetic field is enclosed within Jupiter’s strong magnetic field, creating a unique environment in our solar system for studying magnetic reconnection and other interaction processes. How is Ganymede’s field generated, and how long has it persisted? 5) Ganymede also appears to have an induced magnetic field, which is evidence for a subsurface ocean. Confirmation of the existence of this ocean and its size are important science goals at Ganymede. How has the ocean varied over time, and what is the composition and biological potential of the ocean? 6) The boundary between open and closed magnetic field lines intersecting Ganymede’s surface is clearly visible in color images, showing the effect of different space weathering conditions on the same starting material. How does the magnetic field shield the surface from radiolytic processes, and how can this help us understand processes on the surfaces of unshielded Galilean satellites? 7) Ganymede’s surface is mostly water ice, with evidence for Europa-like hydrated salts and Callisto-like tholins and silicate dust. How variable is the composition of the ice shell? How is the distribution of various non-ice materials related to the surface geology? The Europa Jupiter System Mission currently being planned by NASA and ESA includes a Jupiter Ganymede Orbiter element that would provide us with much of the necessary data to answer the outstanding science questions above. (Acknowledgements to my coauthors on the Decadal Survey Community White Paper on Ganymede science questions)
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