Explaining The Galilean Satellites' Density Gradient By Hydrodynamic Escape.
Abstract
The Galilean satellites exhibit a monotonic trend of decreasing density (increasing ice fraction) with distance from Jupiter. There are three ways this gradient could have been generated. First, it could be the result of a compositional gradient in the proto-jovian disk (the ice line hypothesis) [1]. N-body simulations have found that dynamical mixing within the proto-jovian disk makes this scenario implausible [2]. Second, it could be the result of tidal heating over the lifetime of the satellites [3]. While tidal heating does provide enough energy, little is understood of the physical process that would couple tidal heating to mass loss. Third, is that the ice may have been lost as a part of the accretion process [4]. In this work we suggest hydrodynamic escape powered by the energy of accretion could drive the needed ice loss.
We model the accretion of the forming Galilean satellites following the energy balance method of Kuramoto et al. [4]. We find that when the satellites are forming in a sufficiently high temperature environment a surface ocean will form. This ocean is kept warm by the energy of accretion and will produce a water vapor atmosphere in saturated vapor pressure equilibrium at the surface. This atmosphere is present in an extremely low gravity environment as the satellite is still accreting. This leads to rapid atmospheric mass loss via hydrodynamic escape [5]. We solve for the escape rate using the bounding cases of an isothermal and saturated atmospheric temperature structure. Across our parameter space we consistently find satellites that span the density range observed from Io to Callisto. We will present predictions for the isotopic fractionation this will generate between the existing ice reservoirs of Europa, Ganymede, and Callisto; measurements of plume isotopic ratios by the INMS instrument on Europa Clipper will test our predictions. References: [1] Lunine, J. I., Stevenson, D. J. (1982). Icarus [2] Dwyer, C. A., Nimmo, F., Ogihara, M., Ida, S. (2013). Icarus [3] Canup, R. M., Ward, W. R. (2009) Europa [4] Kuramoto, K., & Matsui, T. (1994). Journal of Geophysical Research: Planets [5] Lehmer, O. R., Catling, D. C., Zahnle, K. J. (2017). The Astrophysical Journal- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P53C3462B
- Keywords:
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- 6218 Jovian satellites;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6299 General or miscellaneous;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5480 Volcanism;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5499 General or miscellaneous;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS