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2005 Annual Science Report

University of California, Los Angeles Reporting  |  JUL 2004 – JUN 2005

From Stars to Genes

Project Summary

Thermal evolution of Io: The thermal equilibrium of a silicate body subject to tidal heating has been studied and applied to the thermal state of Io. The results of this work demonstrate that heat transport in Io is accomplished predominantly by melt segregation and not by convection as previously assumed.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

1. Thermal evolution of Io: The thermal equilibrium of a silicate body subject to tidal heating has been studied and applied to the thermal state of Io. The results of this work demonstrate that heat transport in Io is accomplished predominantly by melt segregation and not by convection as previously assumed. This has a number of consequences for Io’s thermal and rheological structure. Self-consistent models of heat production and melt segregation have been advanced from a simple analysis [Moore, 2001], to a calculation involving convection [Moore, 2003], and are being synthesized into a complete model of melt segregation, tidal heating, and convection in Io [Moore, 2005].

2. Thermal evolution of Europa’s ice shell: Unlike the silicate case, a floating ice shell has only a single, stable equilibrium. Since the internal temperature of the shell is constrained by the melting point at its base, a unique solution for the equilibrium thickness of the shell can be found, given the rheological and physical properties of ice. One of the major advances has been the incorporation of laboratory derived composite flow-laws for ice, including temperature, pressure, stress, and grain-size dependence. Unfortunately, one of these properties, the grain size, is very poorly constrained, and thus a range of thicknesses is possible, depending on the grain size. The minimum thickness is about 15 km (at a grain size of about 1 mm and the current eccentricity), below which the shell is simply too efficient at transporting heat to balance what can be generated by tidal flexing. Obviously, this has strong implications for exploration of the subsurface ocean. At lower eccentricity, this minimum thickness is larger, becoming the thickness of the whole water layer for eccentricities below 0.003, about one third the present value. Eccentricity variations may thus lead to shell thickness variations which become amplified as the eccentricity decreases. This work is currently in press [Moore, 2005].

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  • PROJECT INVESTIGATORS:
    William Moore William Moore
    Unspecified Role
  • RELATED OBJECTIVES:
    Objective 1.1
    Models of formation and evolution of habitable planets

    Objective 1.2
    Indirect and direct astronomical observations of extrasolar habitable planets

    Objective 2.2
    Outer Solar System exploration