Ice collapse over trapped water bodies on Enceladus and Europa

Walker, C. C.; Schmidt, B. E.

doi:10.1002/2014gl062405

Cited by 34 publications

(47 citation statements)

References 42 publications

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“…On Europa dielectric interfaces could also be associated with the boundary between ice and water lenses of eutectic mixtures, fluids in fractures, brine pockets, and refrozen brines, possibly present at a depth of a few kilometers beneath the chaotic regions and ridges [Collins and Nimmo, 2009;Schmidt et al, 2011;Walker and Schmidt, 2015] or in warm ice close to the ocean/ice interface [Chyba et al, 1998].…”

Section: 1002/2014rg000463mentioning

confidence: 99%

Dielectric properties of Jovian satellite ice analogs for subsurface radar exploration: A review

Pettinelli

Cosciotti

Paolo

et al. 2015

Reviews of Geophysics

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The first European mission dedicated to the exploration of Jupiter and its icy moons (JUpiter ICy moons Explorer-JUICE) will be launched in 2022 and will reach its final destination in 2030. The main goals of this mission are to understand the internal structure of the icy crusts of three Galilean satellites (Europa, Ganymede, and Callisto) and, ultimately, to detect Europa's subsurface ocean, which is believed to be the closest to the surface among those hypothesized to exist on these moons. JUICE will be equipped with the 9 MHz subsurface-penetrating radar RIME (Radar for Icy Moon Exploration), which is designed to image the ice down to a depth of 9 km. Moreover, a parallel mission to Europa, which will host onboard REASON (Radar for Europa Assessment and Sounding: Ocean to Near-surface) equipped with 9MHz and 60MHz antennas, has been recently approved by NASA. The success of these experiments strongly relies on the accurate prediction of the radar performance and on the optimal processing and interpretation of radar echoes that, in turn, depend on the dielectric properties of the materials composing the icy satellite crusts. In the present review we report a complete range of potential ice types that may occur on these icy satellites to understand how they may affect the results of the proposed missions. First, we discuss the experimental results on pure and doped water ice in the framework of the Jaccard theory, highlighting the critical aspects in terms of a lack of standard laboratory procedures and inconsistency in data interpretation. We then describe the dielectric behavior of extraterrestrial ice analogs like hydrates and icy mixtures, carbon dioxide ice and ammonia ice. Building on this review, we have selected the most suitable data to compute dielectric attenuation, velocity, vertical resolution, and reflection coefficients for such icy moon environments, with the final goal being to estimate the potential capabilities of the radar missions as a function of the frequency and temperature ranges of interest for the subsurface sounders. We present the different subsurface scenarios and associated radar signal attenuation models that have been proposed so far to simulate the structure of the crust of Europa and discuss the physical and geological nature of various dielectric targets potentially detectable with RIME. Finally, we briefly highlight several unresolved issues that should be addressed, in near future, to improve our capability to produce realistic electromagnetic models of icy moon crusts. The present review is of interest for the geophysical exploration of all solar system bodies, including the Earth, where ice can be present at the surface or at relatively shallow depths.

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Section: 1002/2014rg000463mentioning

confidence: 99%

Dielectric properties of Jovian satellite ice analogs for subsurface radar exploration: A review

Pettinelli

Cosciotti

Paolo

et al. 2015

Reviews of Geophysics

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“…Cryovolcanos (or cryogeysers) would provide relatively easy access to such Europan water, without the need to penetrate the thick, global ice shell. It has also been hypothesized that shallow water reservoirs encased within the ice are related to the formation of chaos terrain, and could lead to localized water vapor venting (Collins & Nimmo 2009;Schmidt et al 2011;Walker & Schmidt 2015). Transient venting may also arise from rapid boiling of cryolavas erupted onto the zero-pressure environment of the Europa surface (Allison & Clifford 1987;Fagents 2003;Quick et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Active Cryovolcanism on Europa?

Sparks

Schmidt

McGrath

et al. 2017

ApJL

Self Cite

152

136

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Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope (HST) using two different observing techniques. Roth et al. (2014) found line emission from the dissociation products of water. Sparks et al. (2016) found evidence for offlimb continuum absorption as Europa transited Jupiter. Here, we present a new transit observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks et al. (2016), raising the possibility of a consistently active source of erupting material on Europa. This conclusion is bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer (PPR) which shows a thermal anomaly at the same location, within the uncertainties (Spencer et al. 1999). The anomaly has 2 the highest observed brightness temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal anomaly, its depth is ≈1.8−2 km, under simple modeling assumptions, consistent with scenarios in which a liquid water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial characterization of Europa's internal water and ice and for seeking evidence of Europa's habitability.

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“…In the analyses presented below, the strength values are set to Y T = 11 kPa and Y S = 15 kPa. Higher strength values, possibly reaching several MPa, have been used in the literature [e.g., Schulson , ; Rudolph and Manga , ; Walker and Schmidt , ]. The relatively low values used here are intended to include the effect of damage due to repeated loading cycles on the ice [ Hammond et al ., ] as well as stress concentration around crack tips [ Schulson and Duval , ].…”

Section: Model Descriptionmentioning

confidence: 99%

The impact of a pressurized regional sea or global ocean on stresses on Enceladus

Johnston

Montési

2017

JGR Planets

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Liquid water is likely present in the interior of Enceladus, but it is still debated whether this water forms a global ocean or a regional sea and whether the present‐day situation is stable. As the heat flux of Enceladus exceeds most heat source estimates, the liquid water is likely cooling and crystallizing, which results in expansion and pressurization of the sea or ocean. We determine, using an axisymmetric Finite Element Model, the tectonic patterns that pressurization of a regional sea or global ocean might produce at the surface of Enceladus. Tension is always predicted above where the ice is thinnest and generates cracks that might be at the origin of the Tiger Stripes. Tectonic activity is also expected in an annulus around the sea if the ice shell is in contact with but slips freely along the rocky core of the satellite. Cracks at the north pole are expected if the shell slips along the core or if there is a global ocean with thin ice at the pole. Water is likely injected along the base of the ice when the shell is grounded, which may lead to cycles of tectonic activity with the shell alternating between floating and grounded states and midlatitude faulting occurring at the transition from a grounded to a floating state.

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Ice collapse over trapped water bodies on Enceladus and Europa

Cited by 34 publications

References 42 publications

Dielectric properties of Jovian satellite ice analogs for subsurface radar exploration: A review

Dielectric properties of Jovian satellite ice analogs for subsurface radar exploration: A review

Active Cryovolcanism on Europa?

The impact of a pressurized regional sea or global ocean on stresses on Enceladus

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