Estimates of Tethys' Present-day Heat Flux and Moment of Inertia from its Long-Wavelength Topography
Abstract
Ocean worlds are important for their implications on planetary evolution and their ability to harbor life [1]. We investigated whether Tethys is an ocean world. The interior structure of a hydrostatic planetary body can be inferred from its long-wavelength (l=2) topography. After accounting for the tidal and rotational contribution, the residual topography is determined largely by isostastic effects [e.g. 2]. There are two types of isostasy: Pratt isostasy wherein topographic variations are the result of density variations in a crust of constant column mass, and Airy isostasy wherein the crust has a constant density but thinner crust is compensated for by the underlying material (be it ocean or mantle). Assuming Pratt isostasy, basal heat flux highs under Tethy's ice shell (its crust) create topographic highs, but assuming Airy they create topographic lows. [3] demonstrated that the spatial heat flux distribution in a planetary body can be described as a linear combination of 3 basis functions. We performed multilinear regressions for the basis function weights required to explain the observed residual topography, given an assumed isostasy type and moment of inertia. These weights depend on whether the interior is rigid or liquid, as well as the depth of this transition. We found the regression fits best for a Tethys that is undergoing Pratt isostasy and obliquity tides, with a solid interior (i.e. no ocean). As Tethys has moderate inclination and small eccentricity, we expected obliquity tidal heating for Tethys [4]. Our regression indicates a present-day surface heat flux of 1.5-2.0 mW/m2, and a normalized moment of inertia of 0.35. This heat flux is an order of magnitude smaller than that inferred for an ancient flexural feature [5]; still, it would either require a highly dissipative interior or a high obliquity to be the result of present-day tidal heating. We also bounded the ice shell thickness using Fourier's law. To be consistent with these constraints, Tethys likely consists of a porous ice outer shell, a solid ice inner shell, and an ice-rock core.
[1] Nimmo & Pappalardo (2016) [2] Hemingway & Matsuyama (2017) [3] Beuthe (2013) [4] Chen et al. (2014) [5] Giese et al. (2007)- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P54B..07G
- Keywords:
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- 6218 Jovian satellites;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 6299 General or miscellaneous;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 5499 General or miscellaneous;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 8147 Planetary interiors;
- TECTONOPHYSICS