Ice diapirs on Europa: Implications for liquid water

341

361

Magnetic field perturbations measured during Galileo flybys of Europa and Callisto are consistent with dipole fields induced by the temporal variations of the ambient jovian magnetospheric field. These fields are close to those expected for perfectly conducting moons. We investigate the implications of these observations for the electrical structure of the moon's interiors using a simple shell model. It is found that Europa and Callisto must possess regions where the conductivity exceeds 0.06 and 0.02 S/m at a depth of less than 200 and 300 km below the surface, respectively. This conductivity is unattainable in ice or silicates, unless the ice layer is at least partially molten or very large temperature gradients can be maintained below the ice. An ionosphere or a cloud of pick-up ions are probably also insufficiently conductive. Global Earth-like oceans under the surface of both moons could account for the observations provided they are at least a few kilometers thick.

Section: Consequences On the Electrical And Physical Structure Of Eurmentioning

confidence: 99%

“…For smaller σ , the insulating crust must be even thinner. Unfortunately, our estimation of the inductive response A is not precise enough to allow us to resolve ice layer thicknesses of the order of 1 or 10 km, as suggested for Europa by Hoppa et al (1999) and Rathbun et al (1998), respectively.…”

Section: Fig 5-continuedmentioning

confidence: 99%

Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations

Zimmer

Khurana

Kivelson

2000

341

361

“…Any chondritic model that has ice forming the only major constituent of the uppermost crust must involve (a) efficient fractional crystallization of brine flows (whereby salts sink and ice floats), (b) some form of solid-state segregation of phases and diapirism, or (c) water evaporation and frost recondensation. There is strong geologic evidence of and theoretical backing for diapirism , Rathbun et al 1998, Spaun et al 1999, McKinnon 1999) and frost condensation , Domingue et al 1991, and fractional crystallization of brines is all but inevitable (Hogenboom et al 1995).…”

Section: Chondrite Evolution Modelsmentioning

confidence: 99%

Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life

Kargel

Kaye

Head

et al. 2000

406

411

We have considered a wide array of scenarios for Europa's chemical evolution in an attempt to explain the presence of ice and hydrated materials on its surface and to understand the physical and chemical nature of any ocean that may lie below. We postulate that, following formation of the jovian system, the europan evolutionary sequence has as its major links: EUROPA'S OCEAN 227 evolution scenarios differ greatly in detailed predictions, but they generally call for a highly impure and chemically layered crust. Some of these models could lead also to lateral chemical heterogeneities by diapiric upwellings and/or cryovolcanism. We describe some plausible geological consequences of the physical-chemical structures predicted from these scenarios. These predicted consequences and observed aspects of Europa's geology may serve as a basis for further analysis and discrimination among several alternative scenarios. Most chemical pathways could support viable ecosystems based on analogy with the metabolic and physiological versatility of terrestrial microorganisms.

“…These processes may have occurred independently of a convective layer. Thus, the modeling of thermally driven ice diapirs by Rathbun et al (1998) does not require (though is compatible with) the occurrence of convection in the ice shell. It is proposed that the heating of shallow lithospheric portions could give rise to mobilization and migration of brines, and contribute to the alteration or even to the disruption of preexistent terrains and to the formation of lenticulae .…”

Section: Lithospheric Heat Flows and Lenticulae Spacingmentioning

confidence: 96%

Heat flow, lenticulae spacing, and possibility of convection in the ice shell of europa

Ruíz

Tejero

2003

Two opposing models to explain the geological features observed on Europa's surface have been proposed. The thin-shell model states that the ice shell is only a few kilometers thick, transfers heat by conduction only, and can become locally thinner until it exposes an underlying ocean on the satellite's surface. According to the thick-shell model, the ice shell may be several tens of kilometers thick and have a lower convective layer, above which there is a cold stagnant lid that dissipates heat by conduction. Whichever the case, from magnetic data there is strong support for the presence of a layer of salty liquid water under the ice. The present study was performed to examine whether the possibility of convection is theoretically consistent with surface heat flows of ϳ100 -200 mW m Ϫ2 , deduced from a thin brittle lithosphere, and with the typical spacing of 15-23 km proposed for the features usually known as lenticulae. It was obtained that under Europa's ice shell conditions convection could occur and also account for high heat flows due to tidal heating of the convective (nearly isothermal) interior, but only if the dominant water ice rheology is superplastic flow (with activation energy of 49 kJ mol Ϫ1 ; this is the rheology thought dominant in the warm interior of the ice shell). In this case the ice shell would be ϳ15-50 km thick. Furthermore, in this scenario explaining the origin of the lenticulae related to convective processes requires ice grain size close to 1 mm and ice thickness around 15-20 km.