Journal ArticleDOI
Convective instability in Europa's floating ice shell
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In this article, the authors apply the temperature-dependent viscosity convection scaling developed by Solomatov and coworkers to the Europan ice shell and find that it is unstable to convection at their base for melting point viscosities of 1013 Pa-s (as linearized by tidal stresses).Abstract:
Models of the tidally heated, floating ice shell proposed for the jovian satellite Europa generally find shell thicknesses less than 30 km. Past parameterized convection models indicated that such shells are stable against convective overturn, which otherwise ostensibly leads to freezing of the ocean underneath. Here I apply the temperature-dependent viscosity convection scaling developed by Solomatov and coworkers to the Europan ice shell. The temperature-dependent properties of ice are linearized about 260 K, as any convective interior should be close to this temperature, with the colder ice forming an essentially passive, stagnant lid. Ice shells ≳ 10 km thick are found to be unstable to convection at their base for melting-point viscosities of 1013 Pa-s (as linearized by tidal stresses), if the ice deforms by superplastic creep, but such low viscosities require small grain sizes (<1 mm). This requirement may be met if grain sizes observed in terrestrial polar glaciers can be strain-rate scaled to Europa. Regardless, convection at the base of the ice shell, if initiated, may not freeze the ocean. Because of tidal heating, a stagnant-lid regime ice shell is much more dissipative than a conductive shell of the same thickness. Such a shell should thin, not thicken, and the potential exists for further thermal instabilities and runaways.read more
Citations
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Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice
TL;DR: Observational evidence for a mid-latitude reservoir of near-surface water ice occupying the pore space of soils is reported and it is inferred that the reservoir was created during the last phase of high orbital obliquity less than 100,000 years ago, and is now being diminished.
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Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life
Jeffrey S. Kargel,Jonathan Z. Kaye,James W. Head,Giles M. Marion,Roger Sassen,James K. Crowley,Olga Prieto Ballesteros,Steven A. Grant,D. L. Hogenboom +8 more
TL;DR: In this article, 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.
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Does Europa have a subsurface ocean? Evaluation of the geological evidence
Robert T. Pappalardo,M. J. S. Belton,H. Herbert Breneman,Michael H. Carr,Clark R. Chapman,Geoffrey C. Collins,Tilmann Denk,Sarah A. Fagents,Paul Geissler,Bernd Giese,Ronald Greeley,Richard Greenberg,James W. Head,Paul Helfenstein,Gregory V. Hoppa,S. D. Kadel,Kenneth P. Klaasen,James E. Klemaszewski,K. Magee,K. Magee,Alfred S. McEwen,Jeffrey M. Moore,William B. Moore,Gerhard Neukum,Cynthia B. Phillips,Louise M. Prockter,Gerald Schubert,David A. Senske,David A. Senske,R. J. Sullivan,B. R. Tufts,Elizabeth P. Turtle,Robert Wagner,K. K. Williams +33 more
TL;DR: In this article, the authors summarize the geological evidence regarding an extant subsurface ocean, concentrating on Galileo imaging data and assess nine pertinent lines of geological evidence: impact morphologies, lenticulae, cryovolcanic features, pull-apart bands, chaos, ridges, surface frosts, topography, and global tectonics.
Journal ArticleDOI
Energetic Ion and Electron Irradiation of the Icy Galilean Satellites
TL;DR: Galileo Orbiter measurements of energetic ions (20 keV to 100 MeV) and electrons (20-700 keV) in Jupiter's magnetosphere are used, in conjunction with the JPL electron model (less than 40 MeV), to compute irradiation effects in the surface layers of Europa, Ganymede, and Callisto as mentioned in this paper.
Journal ArticleDOI
Geological evidence for solid-state convection in Europa's ice shell
Robert T. Pappalardo,James W. Head,Ronald Greeley,Robert Sullivan,Carl B. Pilcher,Gerald Schubert,William B. Moore,Michael H. Carr,Johnnie N. Moore,M. J. S. Belton,David L. Goldsby +10 more
TL;DR: The morphology and geological interpretation of distinct surface features—pits, domes and spots—discovered in high-resolution images of Europa obtained by the Galileo spacecraft are reported, finding that the formation of the features can be explained by thermally induced solid-state convection within an ice shell, possibly overlying a liquid water layer.
References
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Journal ArticleDOI
Scaling of temperature‐ and stress‐dependent viscosity convection
TL;DR: In this article, a simple scaling analysis of temperature and stress-dependent viscosity convection with free-slip boundaries suggests three convective regimes: the small contrast regime, the transitional regime, and the asymptotic regime.
Journal ArticleDOI
Numerical investigation of 2D convection with extremely large viscosity variations
TL;DR: In this article, a finite element multigrid scheme was employed for large viscosity variations and convection with up to 1014 contrasts was systematically investigated in a 2D square cell with free slip boundaries.
Journal ArticleDOI
Geological evidence for solid-state convection in Europa's ice shell
Robert T. Pappalardo,James W. Head,Ronald Greeley,Robert Sullivan,Carl B. Pilcher,Gerald Schubert,William B. Moore,Michael H. Carr,Johnnie N. Moore,M. J. S. Belton,David L. Goldsby +10 more
TL;DR: The morphology and geological interpretation of distinct surface features—pits, domes and spots—discovered in high-resolution images of Europa obtained by the Galileo spacecraft are reported, finding that the formation of the features can be explained by thermally induced solid-state convection within an ice shell, possibly overlying a liquid water layer.
Journal ArticleDOI
Thermal state of an ice shell on Europa
TL;DR: Ojakangas et al. as mentioned in this paper considered a model of Europa consisting of an ice shell that is decoupled from a silicate core by a layer of liquid water, and calculated the thickness of the shell as a function of colatitude and longitude.
Journal ArticleDOI
Influence of a Phase Transition of Ice on the Heat and Mass Balance of Comets
TL;DR: Differences in gas production rates of comets may be explained in part by the phase transition of ice in the comet nuclei.
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