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• -The geology of a newly discovered putative cryovolcanic field is introduced. • -Regional cryotectonic stress fields are reconstructed and compared to global models. • -The potential triggers of cryovolcanic activity in the region is summarized. More and more attention is devoted to the icy moons of the Solar System, including Europa, the second Galilean satellite of Jupiter, since the discovery of potential liquid water and the possibility of extra-terrestrial life harbored in its subsurface ocean below its icy crust. Along with the renaissance of the study of icy satellites, the ongoing missions, such as Europa Clipper and JUICE (JUpiter ICy moons Explorer), are also part of such rejuvenation of icy satellite research. One of the leading research topics connected to Europa is understanding its surface renewal, including the interaction between the subsurface ocean and the icy crust. One of the longest-lasting and still unsettled debates related to Europa is about the nature of the potentially active cryovolcanism, which may play an essential role in the interaction between the surface of the Jovian moon and the underlying subsurface ocean. Our study focuses on the geological-geomorphological characterization of a newly identified putative cryovolcanic field found on the surface of Europa. Various volcanic structures, possibly in multiple stages of maturity, were identified. The executed geological analysis in the surroundings of the volcanoes suggests strong local influence during the formation of cryovolcanic cones working together with the overall global-scale stress fields appearing in the ice crust of Europa. [ABSTRACT FROM AUTHOR]

Despite evidence for plumes on Jupiter's moon Europa, no surface features have been definitively identified as the source of the plumes to date. Furthermore, it remains unknown whether the activity originates from near‐surface water reservoirs within the ice shell or if it is sourced from the underlying global ocean. Here we investigate brine pocket migration, studied previously in the context of sea ice on Earth, as a process for transporting brine along thermal gradients. We show that the fracture system located in the center of Europa's Manannán crater is consistent with the formation of a subsurface brine reservoir. After the initial impact, residual aqueous melt concentrated via brine pocket migration as the target material cooled. Freezing and overpressurization then resulted in a cryovolcanic eruption. The volume of the emptied reservoir and the critical composition at the end of migration provide further constraints on the average salinity of Europa's ice shell. Plain Language Summary: Jupiter's satellite Europa has a subsurface ocean covered by an icy shell. We show how small pockets of brine can migrate within the ice from colder areas to warmer areas. This can happen even at very low temperatures, below the point where pure water would freeze, because the water becomes saltier and saltier as it migrates. By looking at an impact crater on Europa, which was initially warm in the center and cooled inward from its colder surroundings, we can study how the water migrated toward the center and formed a central water reservoir. As the final water pocket at the center of the crater started to freeze, the increasing pressure lead to a cryovolcanic eruption that emplaced brine onto the surface to form a prominent "spider" feature before the ice collapsed into the cavity below. Using a digital terrain model of the crater and collapse feature, we estimate how much water erupted and how salty Europa's ice shell is. Key Points: We introduce brine pocket migration as a mechanism for melt mobilization and a driver for cryovolcanism on icy worldsWe apply brine pocket migration to Europa's Manannán crater and its central "spider" (araneiform) fracture system and collapse structureWe show that understanding the concepts of brine pocket migration can also constrain the salinity of Europa's ice shell and ocean [ABSTRACT FROM AUTHOR]

Jupiter's moon Europa has a relatively young surface (60–90 Myr on average), which may be due in part to cryovolcanic processes. Current models for both effusive and explosive cryovolcanism on Europa may be expanded and enhanced by linking the potential for cryovolcanism at the surface to subsurface cryomagmatism. The success of cryomagma transport through Europa's crust depends critically on the rate of ascent relative to the rate of solidification. The final transport distance of cryomagma is thus governed by initial melt volume, ascent rate, overall ascent distance, transport mechanism (i.e., diapirism, diking, or ascent in cylindrical conduits), and melt temperature and composition. The last two factors are especially critical in determining the budget of expendable energy before complete solidification. Here we use these factors as constraints to explore conditions under which cryomagma may arrive at Europa's surface to facilitate cryovolcanism. We find that 1–5 km radius warm ice diapirs ascending from the base of a 10 km thick stagnant lid can reach the shallow subsurface in a partially molten state. Cryomagma transport may be further facilitated if diapirs travel along pre-heated ascent paths. Under certain conditions, cryolava transported from 10 km depths in tabular dikes or pipe-like conduits may reach the surface at temperatures exceeding 250 K. Ascent rates for these geometries may be high enough that isothermal transport is approached. Cryomagmas containing significant amounts of low eutectic impurities can also be delivered to Europa's surface by propagating dikes or pipe-like conduits. [ABSTRACT FROM AUTHOR]

Europan domes are positive relief features that are typically circular to elliptical in planform shape, and have characteristic diameters <16 km. Although it cannot be ruled out that many of these domes may have been formed from the intrusion of diapirs into Europa's crust, a subset of domes have relatively smooth surfaces that do not mimic the surrounding terrain. These domes appear to obscure the preexisting terrain and have distinct margins which may be lobate or rounded. If all domes on Europa's surface represented structures where the icy crust had simply been "punched up" by diapiric intrusions, uplifts with these distinct morphologies would not be expected to exist. In this study, we revisit the hypothesis that a subset of europan domes formed in a manner similar to lava domes on Earth and Venus. Previously, we modeled dome formation as a consequence of the extrusion of viscous cryolava. However, that approach only allowed for the investigation of late-stage eruptive processes far from the vent and provided little insight into how cryovolcanic fluids may have arrived at the surface. Consideration of cryolava dome emplacement as fluids erupt onto Europa's surface is therefore pertinent. A volume flux approach, in which dome formation is modeled as fluid extrudes onto the surface at a constant rate, has been successfully applied to the formation of lava domes on Venus. That study showed that neglecting to consider changes in fluid rheology while a constant flux of lava is actively extruded onto the surface may result in overestimates, by several orders of magnitude, of initial lava viscosities at the time of eruption. Obtaining accurate viscosity estimates for Europa's cryovolcanic fluids is a critical step in understanding the properties of near-surface fluids that have participated in subsurface-surface exchange in the geologically recent past. To place improved constraints on the rheology and composition of europan cryolavas, and to better gauge the potential for dome formation on Europa via effusive eruptions, we apply this new volume flux approach to the formation of putative europan cryolava domes. We present a perturbation solution to the generalized form of the Boussinesq equation for fluid flow in a cylindrical geometry and explore dome formation while fluid is continuously extruding onto the surface. We find that at the time of eruption, dome-forming cryolavas may have had viscosities of 101–103 Pa s. These viscosity values suggest that cryolavas may be briny slurries composed of a mixture of water, salts, and ice crystals, rather than pure water (viscosity ~10−3 Pa s) or simple brines (viscosities between 10−3 and 10−1 Pa s). Nevertheless, the derived bulk viscosities indicate that dome-forming cryolavas have a rheology more similar to basalt than typical higher-viscosity andesite to rhyolitic dome-forming lavas on Earth. Several of the domes in our study may be connected to liquid reservoirs in Europa's crust, and subsurface-surface exchange may be ongoing today. As such, these domes represent compelling targets for multispectral imaging, radar sounding, and surface sampling by future missions to Europa. • We model the formation of cryolava domes on Europa while fluid is erupting from the vent at a constant rate. • Cryolava viscosities may be on the order of 10–103 Pa s at the time of eruption. • Dome-forming cryolavas may be salty, crystal-rich slurries with a rheology similar to terrestrial basalt. • Cryolava viscosities may represent differences in the thermocompositional states of various subsurface fluid reservoirs. • Cryolava viscosities may be up to 5 orders of magnitude less than those reported from previous modeling. [ABSTRACT FROM AUTHOR]

Abstract: Surface venting is a common occurrence on several outer solar system satellites. Spacecraft have observed plumes erupting from the geologically young surfaces of Io, Triton and Enceladus. Europa also has a relatively young surface and previous studies have suggested that cryovolcanic eruptions may be responsible for the production of low-albedo deposits surrounding lenticulae and along triple band margins and lineae. Here, we have used the projected thicknesses of these deposits as constraints to determine the lifetimes of detectable cryovolcanic plumes that may have emplaced them. In an effort to explore the feasibility of detection of the particle component of plumes by spacecraft cameras operating at visible wavelengths, we present a conservative model to estimate plume characteristics such as height, eruption velocity, and optical depth under a variety of conditions. We find that cryovolcanic plumes on Europa are likely to be fairly small in stature with heights between 2.5 and 26km, and eruption velocities between 81 and 261m/s, respectively. Under these conditions and assuming that plumes are products of steady eruptions with particle radii of 0.5μm, our model suggests that easily detectable plumes will have optical depths, τ, greater than or equal to 0.04, and that their lifetimes may be no more than 300,000 years. Plume detection may be possible if high phase angle limb observations and/or stereo imaging of the surface are undertaken in areas where eruptive activity is likely to occur. Cameras with imaging resolutions greater than 50m/pixel should be used to make all observations. Future missions could employ the results of our model in searches for plume activity at Europa. [Copyright &y& Elsevier]

The surfaces of the Solar System's icy satellites show an extraordinary variety of morphological features, which bear witness to exchange processes between the surface and subsurface. In this paper we review the characteristics of surface features on the moons of Jupiter, Saturn, Uranus and Neptune. Using data from spacecraft missions, we discuss the detailed morphology, size, and topography of cryovolcanic, tectonic, aeolian, fluvial, and impact features of both large moons and smaller satellites. [ABSTRACT FROM AUTHOR]

Images of Europa's surface taken by the Galileo Solid State Imager (SSI) show smooth features measuring a few kilometers, potentially resulting from eruptions of low-viscosity material such as liquid cryomagma. We estimated the volume of four of these smooth features by producing Digital Elevation Models (DEMs) of four Galileo/SSI images. We used the shape-from-shading technique with special care to estimate the uncertainties on the produced DEMs and estimated feature volumes to be between (5.7 ± 0.9) × 1 0 7 m 3 and (2.7 ± 0.4) × 1 0 8 m 3. We discussed the implications for putative sub-surface liquid reservoir dimensions in the case of eruptions induced from freezing reservoirs. Our previous cryovolcanic eruption model was improved by considering a cycle of cryomagma freezing and effusion and by estimating the vaporized cryolava fraction once cryolava spreads onto Europa's surface. Our results show that the cryomagma reservoirs would have to be relatively large to generate these smooth features (1 to 100 km 3 if the flow features result from a single eruption, and 0.4 to 60 km 3 for the full lifetime of a reservoir generating cyclic eruptions). The two future missions JUICE (ESA) and Europa Clipper (NASA) should reach Europa during the late 2020s. They shall give more information on those putative cryovolcanic regions which appear as interesting targets that could provide a better understanding of the material exchanges between the surface, sub-surface and ocean of Europa. • 4 DEMs of smooth features are produced using the AMES StereoPipeline. • Measurements of these feature volumes give 5. 7 ± 0. 9 10 7 to 2. 7 ± 0. 4 10 8 m3. • Cryolava eruption coupled with pre-existing terrain subsidence might generate these features. • 0.4 to 100 km3 cryomagma reservoirs are necessary to put in place the smooth features. [ABSTRACT FROM AUTHOR]