Coupled orbital and thermal evolution of Ganymede

Adam Showman, David J. Stevenson, Renu Malhotra

Research output: Contribution to journalArticle

83 Citations (Scopus)

Abstract

We explore the hypothesis that passage through an eccentricity-pumping resonance could lead to the resurfacing of Ganymede. To do so, we couple R. Malhotra's (1991,Icarus94,399-412) orbital model for the tidal evolution of the Laplace resonance to an internal model of Ganymede. Our model explores the conditions under which Ganymede can undergo global thermal runaway, assuming that theQ/kof Ganymede is strongly dependent on internal temperature. (HereQis the tidal dissipation function andkis the second-degree Love number.) We allow the system to pass through the ω12≈ 2 or ω12≈ 1/2 resonance, where ω1≡ 2n2-n1, ω2≡ 2n3-n2, andn1,n2, andn3are the mean motions of Io, Europa, and Ganymede. If Ganymede's initial internal temperature is either "too hot" or "too cold," no runaway occurs, while for intermediate temperatures (~200 K in the upper mantle), conditions are "just right," and runaway occurs. The range of mantle temperatures that allows runaway depends on the model for tidalQ; we use the Maxwell model, which tiesQto the creep viscosity of ice. Runaways can induce up to ~50-100 K warming and formation of a large internal ocean; they occur over a 107to 108-year period. Assuming carbonaceous chondritic abundances of radionuclides in Ganymede's rocky portion, however, we find that the interior cannot cool to the initial temperatures needed to allow large runaways. If our model is correct, large runaways cannot occur, although small runaways are still possible. Different formulations of tidalQor convective cooling may allow large runaways. Large runaways are also possible if radionuclides are substantially depleted, although this is unlikely. We next consider the consequences of a large runaway, assuming it can occur. Ganymede can undergo 0.5% thermal expansion (by volume) during the largest thermal runaways. Melting of the ice mantle provides up to 2% expansion despite the fact that contraction produced by melting ice I offsets expansion produced by melting high-pressure ice phases. Solid-solid phase transitions cause negligible satellite expansion. Lithospheric stresses caused by expansion of 2% over 107to 108years are ~102bars at the surface, and drop to a few bars at several kilometers depth. Such stresses could cause cracking to depths of several kilometers. The cracking and near-surface production of warm or partially molten ice make resurfacing a plausible outcome of a large thermal runaway. The tidal heating events proposed here may also be relevant for generation of Ganymede's modern-day magnetic field.

Original languageEnglish (US)
Pages (from-to)367-383
Number of pages17
JournalIcarus
Volume129
Issue number2
DOIs
StatePublished - Oct 1997
Externally publishedYes

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Ganymede
thermal evolution
orbitals
ice
Earth mantle
expansion
melting
temperature
radioactive isotopes
radionuclide
pressure ice
mantle
Europa
Io
heating
causes
thermal expansion
phase transition
eccentricity
creep

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Coupled orbital and thermal evolution of Ganymede. / Showman, Adam; Stevenson, David J.; Malhotra, Renu.

In: Icarus, Vol. 129, No. 2, 10.1997, p. 367-383.

Research output: Contribution to journalArticle

Showman, Adam ; Stevenson, David J. ; Malhotra, Renu. / Coupled orbital and thermal evolution of Ganymede. In: Icarus. 1997 ; Vol. 129, No. 2. pp. 367-383.
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