Thermal state of an ice shell on Europa

Ojakangas, G. W.; Stevenson, D. J.

doi:10.1016/0019-1035(89)90052-3

Cited by 326 publications

(404 citation statements)

References 27 publications

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“…where c(T ), r(T ) and k(T ) are specific heat, density and thermal conductivity, respectively (temperature dependencies given in [Ojakangas and Stevenson, 1989]). The term q(T ) represents a temperature dependent volumetric heating due to tidal flexure of the icy shell.…”

Section: Introductionmentioning

confidence: 99%

Persistence of thin ice regions in Europa's ice crust

Buck

Chyba

Goulet

et al. 2002

Geophysical Research Letters

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[1] Extensive data from planetary spacecraft as well as celestial mechanics models support the existence of a subsurface ocean on Europa $100 km thick, maintained by a tidal heat flux. Models in which the overlying ice crust is less than 20 km thick permit breaches in the ice due to impact events or thermal plumes from the tidally heated core. We apply a two-dimensional thermal model to the analysis of the refreezing of a hole in the ice crust following a breach event. Our model incorporates heat produced by tidal heating of Europa in two ways: a basal heat flux from Europa's silicate and iron core, together with volumetric heating of the ice shell. We compare our refreezing timescales to those obtained from a model where viscous flow in the base of the ice crust fills the hole. We find that catastrophic breaches in Europa's ice crust may produce regions of relatively thin ice persisting up to $1 My. These breaches are closed by viscous flow when radii are small (<10-50 km) and by conductive refreezing for larger radii, especially if Europa's crust has a high basal heat flow due to a hot core. Detection of the ice/ocean interface by orbital detection of the temperature anomalies or radar sounding would be most probable in the vicinity of these events.

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Section: Introductionmentioning

confidence: 99%

Persistence of thin ice regions in Europa's ice crust

Buck

Chyba

Goulet

et al. 2002

Geophysical Research Letters

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“…Although the viscosity contrast across the entire ice shell can be very large, the viscosity variation within the convective sublayer is typically of one order of magnitude [see Grasset and Parmentier (1998) Ruiz et al 2007). This is useful for Europa, because tidal heating is strongly temperature-depedent (Ojakangas and Stevenson 1989), and it is largely restricted to the warmest ice. In these conditions, tidal heating is negligible in the stagnant lid, which can be treated separately (Hussmann et al 2002;Ruiz and Tejero 2003).…”

Section: Convective Modelmentioning

confidence: 99%

“…where T s is the surlace temperature, taken as 100 K, a value considered as representative of the mean temperature at Europa's surface (e.g., Ojakangas and Stevenson 1989). Finally, to calculate tidal heating rates, I assume that llllder tidal stresses ice behave like a viscoelastic (Maxwell) material: thus, the tidal volumetric dissipation rate can be cal culated according to (Ojakangas and Stevenson 1989) …”

Section: Convective Modelmentioning

confidence: 99%

“…Finally, to calculate tidal heating rates, I assume that llllder tidal stresses ice behave like a viscoelastic (Maxwell) material: thus, the tidal volumetric dissipation rate can be cal culated according to (Ojakangas and Stevenson 1989) …”

Section: Convective Modelmentioning

confidence: 99%

“…where 8 is the strain rate, here taken as 2 x 10-1 0 s-I , value considered as representative for the average strain rate on the icy shell of Europa (Ojakangas and Stevenson 1989;McKinnon 1999), f1 = 4 X 109 Pa is the ice rigidity, and w is the frequency of the forcing, which can be equated with Europa's mean motion, 2.05 x 10-5 rad S-l. I take H = H i , which somewhat overestimates tidal dissipation within the upper bOlmdary layer (where temperatures are lower than T i )' temperatures are higher than T i ) total tidal heating.…”

Section: Convective Modelmentioning

confidence: 99%

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Equilibrium Convection on a Tidally Heated and Stressed Icy Shell of Europa for a Composite Water Ice Rheology

Ruíz

2010

Earth Moon Planets

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Water ice I rheology is akey factorfor llllderstanding the thermal and mechanical state of the outer shell of the icy satellites. Ice flow involves several deformation mechanisms (both Newtonian and non-Newtonian), which contribute to different extents depending on the temperature, grain size, and applied stress. In this work I analyze tidally heated and stressed equilibrium convection in the ice shell of Europa by considering a composite viscosity law which includes diffusion creep, basal slip, grain bOlmdary sliding and dislo cation creep, and. The calculations take into aCcOllllt the effect of tidal stresses on ice flow and use grain sizes between 0.1 and 100 mm. An Arrhenius-type relation (useful for parameterized convective models) is fOlllld then by fi tting the calculated viscosity between 170 and 273 K to an exponential regression, which can be expressed in terms of pre exponential constant and effective activation energy.

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The effects of laterally varying icy shell structure on the tidal response of Ganymede and Europa

Wahr

Zhong

2014

JGR Planets

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We use a finite-element model to solve for the response of Ganymede and Europa to tidal forcing from Jupiter, using various icy shell models with laterally variable (3-D) structure. In all cases, the shell is assumed to be underlain by a liquid-water ocean. Icy shells with laterally varying thickness are derived from a thermal conduction model. Three-dimensional shear modulus profiles for the shell are built either from a conduction model or, for Europa, by assuming a hemispherical difference in composition. Icy shell structures with a nonglobal ocean are built for Ganymede. Using these shell structures to calculate the tidal response of Ganymede and Europa, we conclude the following: (1) the presence of lateral variations in thickness or in shear modulus would not degrade future attempts to use tidal observations to decide on the existence or absence of a liquid ocean and to determine the mean icy shell thickness. (2) Given accurate enough observations, the presence of lateral variations in thickness or in shear modulus could be determined by searching for nondegree-2 components in the tidal response. (3) In the absence of significant viscous convective flow in the shell, the effects of a laterally varying shear modulus on the tidal response would be smaller than those of a laterally varying shell thickness. (4) If the shell is partially grounded, tidal observations of either gravity or uplift would be able to roughly differentiate regions where the ice is grounded from those where it is floating.

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Thermal state of an ice shell on Europa

Cited by 326 publications

References 27 publications

Persistence of thin ice regions in Europa's ice crust

Persistence of thin ice regions in Europa's ice crust

Equilibrium Convection on a Tidally Heated and Stressed Icy Shell of Europa for a Composite Water Ice Rheology

The effects of laterally varying icy shell structure on the tidal response of Ganymede and Europa

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