HR: 14:55h
AN: P53A-06    [Abstracts]
TI: Hydrothermal Circulation in Europa's Mantle
AU: * Travis, B
EM: bjtravis@lanl.gov
AF: Earth and Environmental Sciences Div., Los Alamos National Laboratory, EES-2/MS-F665, Los Alamos, NM 87545 United States
AU: Schubert, G
EM: schubert@ucla.edu
AF: Dept. of Earth and Space Sciences, University of California, Los Angeles, 595 Charles E. Young Dr. E., Los Angeles, CA 90095 United States
AU: Palguta, J
EM: jpalguta@ucla.edu
AF: Dept. of Earth and Space Sciences, University of California, Los Angeles, 595 Charles E. Young Dr. E., Los Angeles, CA 90095 United States
AB: Features on the surface of Europa may reflect non-uniform heating in an underlying ocean due to variations in heat flux at the top of the mantle. Pore water convection can generate a spatially heterogeneous heat flux in a fractured, permeable mantle. Continual stressing of mantle material by gravitational tides, as well as occasional large-scale freezing and thawing that might be associated with changes in tidal resonance, and long-term hydration/dehydration processes, may allow significant permeability to exist despite the approximately 1 kbar confining overburden pressure at the mantle surface. We use a computational model of Europa to determine the impact of hydrothermal convection on overall heat transport, ice shell thickness, and heat flux heterogeneity and magnitude at the mantle/ocean and ocean/ice shell interfaces. Our model of Europa includes a core, a silicate mantle, an ocean layer, and an ice shell. Hydrothermal convection in the mantle, thermal diffusion, parameterized ocean flow and melting/freezing are the heat transport mechanisms included. Surface temperatures range sinusoidally from 52K at the poles to 110K at the equator. Total heating in the body consists of tidal dissipation in the mantle and core, radiogenic heating in the mantle, and tidal dissipation in the ice shell. Tidal heating is a function of ice viscosity and pressure-dependent melt temperature. Literature values for the total heating range from about 1 to 10 TW. Mantle and core heating are estimated to be equivalent to about 10 mW/m² at the mantle surface. We assume that the outer few hundred kilometers of the mantle are permeable, and use an average value of 10 millidarcys, typical of the Earth at equivalent overburden depths. In 2-D and 3-D simulations, the ice shell thickness ranges from 20 km or less at the equator to about 40 km at the poles, with a slushy ice/water mixture below the ice cap in the polar regions. Transient, well-defined plumes are seen in the equatorial region (roughly +/- 30^o) of the ocean layer, leading to enhanced heat flux below the ice cap there. Vigorous convection occurs in the mantle as a mix of plumes and linear features roughly 25-100 km wide and lengths up to several hundred kilometers. Changes in dynamics as a function of mantle permeability and heating rates are being explored. This work was supported by a grant from the Institute of Geophysics and Planetary Physics at Los Alamos National Laboratory and by the NASA Planetary Geology and Geophysics Program.
DE: 0560 Numerical solutions (4255)
DE: 1800 HYDROLOGY
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
DE: 5430 Interiors (8147)
DE: 6221 Europa
SC: Planetary Sciences [P]
MN: Fall Meeting 2005