Active Cryovolcanism on Europa?

Sparks, W. B.; Schmidt, B. E.; McGrath, M. A.; Hand, K. P.; Spencer, J. R.; Cracraft, M.; Deustua, Susana E.

doi:10.3847/2041-8213/aa67f8

Cited by 152 publications

(142 citation statements)

References 37 publications

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“…However, it is interesting that the area associated with the Galileo nighttime thermal excess is actually colder in the ALMA data than the model predicts. For the Galileo PPR observation, shown in Figure 2 alongside the best-fit model image and the resulting residuals, the same location is indeed anomalously warm, as noted by Spencer et al (1999) and Sparks et al (2017). In fact, the entire Pwyll Crater region, not just the potential plume source location slightly northwest of the crater, shows up as anomalously hot at night and cold during the day.…”

Section: Fits To Alma and Galileo Ppr Observationsmentioning

confidence: 81%

“…An elevated thermal inertia near Pwyll Crater and the anomaly in question, as originally noted by Spencer et al (1999), may result from higher average regolith particle sizes in the ejecta blanket. This possibility seems particularly plausible as the anomalous temperatures are not just constrained to the relatively small potential plume source area (Sparks et al 2017), but are observed across the entirety of the Pwyll region (Figures 1 and 2). Spencer et al (1999) also suggest the possibility that impact-exposed water ice may allow for deeper sunlight penetration, which, as discussed in Section 3, can mimic the effects of increased thermal inertia.…”

Section: Fits To Alma and Galileo Ppr Observationsmentioning

confidence: 99%

“…If such activity continued today, then direct study of the oceanic composition may be possible, but the question of modern geologic activity remains. Recent observations using the Hubble Space Telescope (HST) have hinted at the possibility of active water vapor plumes at Europa (Roth et al 2014a(Roth et al , 2014bSparks et al 2016Sparks et al , 2017. However, the detections have been sporadic and tenuous, making confirming the existence of plumes difficult.…”

Section: Introductionmentioning

confidence: 99%

“…We simulate an area 156 km in radius (corresponding to our ALMA resolution in this region) centered on 276°W and 16°. 8 S, which is coincident with the Galileo thermal anomaly in the potential plume source region (Sparks et al 2016(Sparks et al , 2017. We model the case of an endogenic thermal anomaly by raising the geothermal heat flux beneath the lowest layer of our simulation (five diurnal skin depths ≈0.75 m at our best-fit parameters).…”

Section: Fits To Alma and Galileo Ppr Observationsmentioning

confidence: 99%

“…Therefore, high-resolution thermal data may present another, perhaps more robust, way of identifying active regions in the case of Europa. Sparks et al (2016Sparks et al ( , 2017 detected potential off-limb absorption near the crater Pwyll in HST images of Europa as it transited Jupiter. This location is coincident with a nighttime thermal excess in brightness temperatures measured by the Galileo Photopolarimeter Radiometer (PPR; Spencer et al 1999;Moore et al 2009).…”

Section: Introductionmentioning

confidence: 99%

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ALMA Thermal Observations of a Proposed Plume Source Region on Europa

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Brown

Butler

2017

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We present a daytime thermal image of Europa taken with the Atacama Large Millimeter Array. The imaged region includes the area northwest of Pwyll Crater, which is associated with a nighttime thermal excess seen by the Galileo Photopolarimeter Radiometer and with two potential plume detections. We develop a global thermal model of Europa and simulate both the daytime and nighttime thermal emission to determine if the nighttime thermal anomaly is caused by excess endogenic heat flow, as might be expected from a plume source region. We find that the nighttime and daytime brightness temperatures near Pwyll Crater cannot be matched by including excess heat flow at that location. Rather, we can successfully model both measurements by increasing the local thermal inertia of the surface.

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Section: Fits To Alma and Galileo Ppr Observationsmentioning

confidence: 81%

Section: Fits To Alma and Galileo Ppr Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Fits To Alma and Galileo Ppr Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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ALMA Thermal Observations of a Proposed Plume Source Region on Europa

Trumbo

Brown

Butler

2017

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Expected Seismicity and the Seismic Noise Environment of Europa

et al. 2018

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Seismic data will be a vital geophysical constraint on internal structure of Europa if we land instruments on the surface. Quantifying expected seismic activity on Europa both in terms of large, recognizable signals and ambient background noise is important for understanding dynamics of the moon, as well as interpretation of potential future data. Seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans. We define a range of models of seismic activity in Europa's ice shell by assuming each model follows a Gutenberg‐Richter relationship with varying parameters. A range of cumulative seismic moment release between 1016 and 1018 Nm/yr is defined by scaling tidal dissipation energy to tectonic events on the Earth's moon. Random catalogs are generated and used to create synthetic continuous noise records through numerical wave propagation in thermodynamically self‐consistent models of the interior structure of Europa. Spectral characteristics of the noise are calculated by determining probabilistic power spectral densities of the synthetic records. While the range of seismicity models predicts noise levels that vary by 80 dB, we show that most noise estimates are below the self‐noise floor of high‐frequency geophones but may be recorded by more sensitive instruments. The largest expected signals exceed background noise by ∼50 dB. Noise records may allow for constraints on interior structure through autocorrelation. Models of seismic noise generated by pressure variations at the base of the ice shell due to turbulent motions in the subsurface ocean may also generate observable seismic noise.

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Entrainment and Dynamics of Ocean-derived Impurities within Europa's Ice Shell

Buffo

Schmidt

Huber

et al. 2020

Preprint

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Compositional heterogeneities within Europa's ice shell likely impact the dynamics and habitability of the ice and subsurface ocean, but the total inventory and distribution of impurities within the shell are unknown. In sea ice on Earth, the thermochemical environment at the ice-ocean interface governs impurity entrainment into the ice. Here, we simulate Europa's ice-ocean interface and bound the impurity load (1.053-14.72 g/kg [parts per thousand weight percent, or ppt] bulk ice shell salinity) and bulk salinity profile of the ice shell. We derive constitutive equations that predict ice composition as a function of the ice shell thermal gradient and ocean composition. We show that evolving solidification rates of the ocean and hydrologic features within the shell produce compositional variations (ice bulk salinities of 5-50% of the ocean salinity) that can affect the material properties of the ice. As the shell thickens, less salt is entrained at the ice-ocean interface, which implies Europa's ice shell is compositionally homogeneous below~1 km. Conversely, the solidification of water filled fractures or lenses introduces substantial compositional variations within the ice shell, creating gradients in mechanical and thermal properties within the ice shell that could help initiate and sustain geological activity. Our results suggest that ocean materials entrained within Europa's ice shell affect the formation of geologic terrain and that these structures could be confirmed by planned spacecraft observations. Plain Language Summary Europa, the second innermost moon of Jupiter, likely houses an interior ocean that could provide a habitat for life. This ocean resides beneath a 10-to >30-km-thick ice shell which could act as a barrier or conveyor for ocean-surface material transport that could render the ocean chemistry either hospitable or unfavorable for life. Additionally, material impurities in the ice shell will alter its physical properties and thus affect the global dynamics of the moon's icy exterior. That said, few of the interior properties of the ice shell or ocean have been directly measured. On Earth, the composition of ocean-derived ice is governed by the chemistry of the parent liquid and the rate at which it forms. Here, we extend models of sea ice to accommodate the Europa ice-ocean environment and produce physically realistic predictions of Europa's ice shell composition and the evolution of water bodies (fractures and lenses) within the shell. Our results show that the thermal gradient of the ice and the liquid composition affect the formation and evolution of geologic features in ways that could be detectable by future spacecraft (e.g., by ice penetrating radar measurements made by Europa Clipper).

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Active Cryovolcanism on Europa?

Cited by 152 publications

References 37 publications

ALMA Thermal Observations of a Proposed Plume Source Region on Europa

ALMA Thermal Observations of a Proposed Plume Source Region on Europa

Expected Seismicity and the Seismic Noise Environment of Europa

Entrainment and Dynamics of Ocean-derived Impurities within Europa's Ice Shell

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