Constraints on Enceladus' Interior from Cassini Observations - Requirements for Future Geophysical Investigations

Details Constraints on Enceladus' Interior from Cassini Observations - Requirements for Future Geophysical Investigations Constraints on Enceladus' Interior from Cassini Observations - Requirements for Future Geophysical Investigations

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p13b0170c&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P13B-0170

Mathematics

Logic

6024 Interiors (8147), 6035 Orbital And Rotational Dynamics, 6280 Saturnian Satellites, 6297 Instruments And Techniques

Scientific paper

We review the constraints on Enceladus' interior inferred from multi-instrument observations by the Cassini Orbiter. Available surface temperature mapping, shape data and geological imaging indicate that the body presents large lateral variations in internal viscoelastic properties, which makes it greatly non-hydrostatic. We will present geophysical evidence that the satellite is differentiated and that there cannot be a global ocean inside Enceladus, but that most probably liquid is located under young surfaces only. Temperature measurements and geyser modeling indicate that the water ice melting point could be reached a few tens meters under the South pole surface (Spencer et al. 2006; Porco et al. 2006). However, this is not enough to conclude that there is a liquid layer immediately below the surface. Water ice could be at the melting point. Different models in development show that a hotspot localized under the South pole, at a temperature close to the water ice melting point may be able to explain the power radiated from the "South pole area" (e.g., Tobie and Cadek, Europlanet Conference 2006; Castillo et al., submitted) and why this exceptional region is located at the South pole (Nimmo and Pappalardo, Nature 441, 614, 2006). The models provide a basis for specifying measurements needed for further investigation of Enceladus' interior from an orbiter and/or a lander. Gravity measurements from Doppler tracking and ranging are necessary to provide information on the distribution of density. The degree-two component J¬2 ranges from 5.2x10e-3 to 7.8x10e-3 as a function of the degree of differentiation and the silicate density, assuming the satellite is in hydrostatic equilibrium. The dynamical term of the degree-two gravity component (function of the potential tidal Love number k2) is ~10e-7. If Enceladus' shape deviates from hydrostatic equilibrium by 1 or 2 km, it is going to make gravity observations difficult to interpret. Assuming that the South pole is relaxed (because its mechanical lithosphere is expected to be thin) it would be the best place to fly over in order to get information on the deep interior from gravity measurements. Coupled gravity and altimetric measurements with a high spatial resolution are then necessary to better constrain the internal dynamics of the satellite. Full surface temperature coverage, especially during nighttime, is crucial to better assess the distribution of heat sources total heat flow. This work was carried out at the Jet Propulsion Laboratory-California Institute of Technology, under contract to NASA.

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