Effects of plasticity on convection in an ice shell: Implications for Europa

Showman, Adam P.; Han, Lei

doi:10.1016/j.icarus.2005.02.020

Cited by 56 publications

(69 citation statements)

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“…One problem with diapirism is that the heat in the rising plume must not diffuse until it reaches the surface area, in order to maintain sufficient buoyancy. Furthermore, detailed numerical calculations revealed that it is difficult to reproduce the observed morphology through a thermal diapir mechanism [ Showman and Han , , ]. In addition to thermal buoyancy, compositional buoyancy can generate a diapir [ Pappalardo and Barr , ; Han and Showman , ]; a compositional density difference actually generates a larger buoyancy than thermal diapirism.…”

Section: Introductionmentioning

confidence: 99%

Compositional diapirism as the origin of the low‐albedo terrain and vaporization at midlatitude on Ceres

Dake

Kurita

2014

JGR Planets

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Recent observations of Ceres, made using the Heterodyne Instrument for the Far Infrared on board the European Space Agency's Herschel Space Observatory, have shown that water vapor is emanated from the low‐albedo midlatitude regions. Based on the supposition that some dark spots on Europa may be caused by diapirism, we explored whether Ceres' environment also can induce compositional diapirism, and whether an upwelling diapir could explain the origin and distribution of the dark spots and vaporization of Ceres. If the density of the rock that constitutes Ceres is around 2700 kg m−3, the undifferentiated crust is stable over geological time periods at less than 180 K. At a surface temperature of 170 K, a diapir can reach the surface if the crust is a few tens of kilometers thick. Alternatively, if the surface temperature is 150 K, a large contrast in viscosity would prevent diapirs from reaching the surface. The relatively moderate surface temperature in the midlatitude regions of Ceres may be the reason for the formation of dark terrains occurring only in such areas. Our finite difference calculations do not show that diapirism melts the surface ice because the temperature gradient changes very little. However, if the observed vapor emission is caused by the sublimation of fresh ice, compositional diapirism could be the mechanism that transports the fresh ice to the surface. In addition to other mechanisms such as cryovolcanism, diapirism is a valid hypothesis for explaining the dark terrain and vapor emissions of Ceres.

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Section: Introductionmentioning

confidence: 99%

Compositional diapirism as the origin of the low‐albedo terrain and vaporization at midlatitude on Ceres

Dake

Kurita

2014

JGR Planets

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“…The putative regular spacing was never confirmed. Moreover, the characteristics attributed to ''pits, spots, and domes'' were not consistent with numerical models of convection (Showman and Han, 2005).…”

Section: Greenbergmentioning

confidence: 71%

Exploration and Protection of Europa's Biosphere: Implications of Permeable Ice

Greenberg

2011

Astrobiology

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Europa has become a high-priority objective for exploration because it may harbor life. Strategic planning for its exploration has been predicated on an extreme model in which the expected oceanic biosphere lies under a thick ice crust, buried too deep to be reached in the foreseeable future, which would beg the question of whether other active satellites might be more realistic objectives. However, Europa's ice may in fact be permeable, with very different implications for the possibilities for life and for mission planning. A biosphere may extend up to near the surface, making life far more readily accessible to exploration while at the same time making it vulnerable to contamination. The chances of finding life on Europa are substantially improved while the need for planetary protection becomes essential. The new National Research Council planetary protection study will need to go beyond its current mandate if meaningful standards are to be put in place.

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“…Whilst these effects may be negligible on other planets (where the ocean makes up a smaller proportion of the radius), their effects should be quantitatively assessed using the methods of this paper so that any neglect of such effects can be justified or shown to be questionable. This procedure is also applicable to the modelling of non-acoustic phenomena such as heat convection, mass flux, and glacial/tectonic interaction (Lee et al, 2003;Showman and Han, 2005). Such justification for neglecting relevant physics should not be based on misleading comparisons between the systematic sound speed discrepancies described in this paper, and the current uncertainties in the values of other parameters (e.g., ocean temperature and salinity variations) whose physics is correctly incorporated into the models but whose values are estimated with uncertainty which may be reduced as further data becomes available.…”

Section: Discussionmentioning

confidence: 99%