Cryovolcanic emplacement of domes on Europa

Cryovolcanic emplacement of domes on Europa

Authors:

Quick et al

Abstract:

Here we explore the hypothesis that certain domes on Europa may have been produced by the extrusion of viscous cryolavas. A new mathematical method for the emplacement and relaxation of viscous lava domes is presented and applied to putative cryovolcanic domes on Europa. A similarity solution approach is applied to the governing equation for fluid flow in a cylindrical geometry, and dome relaxation is explored assuming a volume of cryolava has been rapidly emplaced onto the surface. Nonphysical singularities inherent in previous models for dome relaxation have been eliminated, and cryolava cooling is represented by a time-variable viscosity. We find that at the onset of relaxation, bulk kinematic viscosities may lie in the range between 103 and 106 m2/s, while the actual fluid lava viscosity may be much lower. Plausible relaxation times to form the domes, which are linked to bulk cryolava rheology, are found to range from 3.6 days to 7.5 years. We find that cooling of the cryolava, while dominated by conduction through an icy skin, should not prevent fluids from advancing and relaxing to form domes within the timescales considered. Determining the range of emplacement conditions for putative cryolava domes will shed light on Europa's resurfacing history. In addition, the rheologies and compositions of erupted cryolavas have implications for subsurface cryomagma ascent and local surface stress conditions on Europa.

Evidence of Cryovolcanism on Europa in the Argadnel Regio

Surface composition of pull-apart bands in Argadnel Regio, Europa: Evidence of localized cryovolcanic resurfacing during basin formation

Authors:

Prockter et al

Abstract:

We combine Galileo Solid State Imager (SSI) and Near-Infrared Mapping Spectrometer (NIMS) data to investigate the composition of pull-apart bands in Europa's Argadnel Regio. Using spectral linear mixture modeling employing cryogenic laboratory reference spectra, we find that bands of intermediate age (“grey” bands) are compositionally distinct from bands that are stratigraphically younger (“dark” bands). The grey bands have higher abundances of larger ice grains and lower abundances of hydrated salts than the dark bands; both of these tendencies are statistically significant at the 1% level. The grey and dark bands have similar abundances of hexahydrite, a material which is relatively stable under irradiation; however, the derived abundances of frozen magnesium sulfate brine and of mirabilite, which are more susceptible to fragmentation by radiation, are significantly higher in the dark bands than in the grey bands. These results are consistent with a physical model in which the differences in composition and in ice grain sizes are linked to space weathering and radiolytic processing levels; the grey bands have presumably undergone higher levels of processing, due to being exposed on Europa's surface for a longer period of time. One prominent wedge-shaped band exhibits an anomalous albedo variation across its northern portion, appearing dark in its top third, and grey in its southernmost two-thirds. We find that the dark part of the band has a modeled composition that is in-family with other dark bands, while the grey portion has a modeled composition that is indistinguishable from other grey bands in the study area. Because these variations cannot easily be attributed to the band's formation mechanism (bands open sequentially along a central axis), we surmise that the northern part has been resurfaced, probably in response to the formation of a large topographic basin that cuts through the band. Faulting accompanying basin formation may provide conduits allowing transport to the surface of materials from Europa's interior. We hypothesize that the formation of the basin resulted in fresh cryovolcanic material being deposited across the northern portion of the band, effectively “resetting” its surface age. If, as has been suggested, the giant arcuate basins resulted from an episode of true polar wander, our study may help to more tightly constrain the age of that event within Europa's geologic column.

Cryovolcanism Took Place on Ceres Since the Start of the Triassic

Cryovolcanism on Ceres

Authors:

Ruesch et al

Abstract:

INTRODUCTION

Classic volcanism prevalent on terrestrial planets and volatile-poor protoplanets, such as asteroid Vesta, is based on silicate chemistry and is often expressed by volcanic edifices (unless erased by impact bombardment). In ice-rich bodies with sufficiently warm interiors, cryovolcanism involving liquid brines can occur. Smooth plains on some icy satellites of the outer solar system have been suggested as possibly cryovolcanic in origin. However, evidence for cryovolcanic edifices has proven elusive. Ceres is a volatile-rich dwarf planet with an average equatorial surface temperature of ~160 K. Whether this small (~940 km diameter) body without tidal dissipation could sustain cryovolcanism has been an open question because the surface landforms and relation to internal activity were unknown.

RATIONALE

The Framing Camera onboard the Dawn spacecraft has observed >99% of Ceres’ surface at a resolution of 35 m/pixel at visible wavelengths. This wide coverage and resolution were exploited for geologic mapping and age determination. Observations with a resolution of 135 m/pixel were obtained under several different viewing geometries. The stereo-photogrammetric method applied to this data set allowed the calculation of a digital terrain model, from which morphometry was investigated. The observations revealed a 4-km-high topographic relief, named Ahuna Mons, that is consistent with a cryovolcanic dome emplacement.

RESULTS

The ~17-km-wide and 4-km-high Ahuna Mons has a distinct size, shape, and morphology. Its summit topography is concave downward, and its flanks are at the angle of repose. The morphology is characterized by (i) troughs, ridges, and hummocky areas at the summit, indicating multiple phases of activity, such as extensional fracturing, and (ii) downslope lineations on the flanks, indicating rockfalls and accumulation of slope debris. These morphometric and morphologic observations are explained by the formation of a cryovolcanic dome, which is analogous to a high-viscosity silicic dome on terrestrial planets. Models indicate that extrusions of a highly viscous melt-bearing material can lead to the buildup of a brittle carapace at the summit, enclosing a ductile core. Partial fracturing and disintegration of the carapace generates slope debris, and relaxation of the dome’s ductile core due to gravity shapes the topographic profile of the summit. Modeling of this final phase of dome relaxation and reproduction of the topographic profile requires an extruded material of high viscosity, which is consistent with the mountain’s morphology. We constrained the age of the most recent activity on Ahuna Mons to be within the past 210 ± 30 million years.

CONCLUSION

Cryovolcanic activity during the geologically recent past of Ceres constrains its thermal and chemical history. We propose that hydrated salts with low eutectic temperatures and low thermal conductivities enabled the presence of cryomagmatic liquids within Ceres. These salts are the product of global aqueous alteration, a key process for Ceres’ evolution as recorded by the aqueously altered, secondary minerals observed on the surface.

The Geology (Hadeology) of Pluto and Charon Through the Eyes of New Horizons

The Geology of Pluto and Charon Through the Eyes of New Horizons

Authors:

Moore et al

Abstract:

NASA's New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Pluto's encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than ≈10 Ma. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, likely by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic, and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 Ga old that are extensionally fractured and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest proposed impactor size-frequency distributions proposed for the Kuiper belt.

Cryolava flow destabilization of crustal methane clathrate hydrate on Titan

Cryolava flow destabilization of crustal methane clathrate hydrate on Titan

Authors:

Davies et al

Abstract:

To date, there has been no conclusive observation of ongoing endogenous volcanic activity on Saturn's moon Titan. However, with time, Titan's atmospheric methane is lost and must be replenished. We have modeled one possible mechanism for the replenishment of Titan's methane loss. Cryolavas can supply enough heat to release large amounts of methane from methane clathrate hydrates (MCH). The volume of methane released is controlled by the flow thickness and its areal extent. The depth of the destabilisation layer is typically ≈30% of the thickness of the lava flow (≈3 m for a 10-m thick flow). For this flow example, a maximum of 372 kg of methane is released per m2 of flow area. Such an event would release methane for nearly a year. One or two events per year covering ∼20 km2 would be sufficient to resupply atmospheric methane. A much larger effusive event covering an area of ≈9000 km2 with flows 200 m thick would release enough methane to sustain current methane concentrations for 10,000 years. The minimum size of “cryo-flows” sufficient to maintain the current atmospheric methane is small enough that their detection with current instruments (e.g., Cassini) could be challenging. We do not suggest that Titan's original atmosphere was generated by this mechanism. It is unlikely that small-scale surface MCH destabilisation is solely responsible for long-term (greater than a few Myr) sustenance of Titan's atmospheric methane, but rather we present it as a possible contributor to Titan's past and current atmospheric methane.

Detecting volcanism on Titan and Venus with microwave radiometry

Detecting volcanism on Titan and Venus with microwave radiometry

Authors:

Lorenz et al

Abstract:

The detection by spaceborne instrumentation of infrared thermal emission from volcanic eruptions is well-established on Earth, but is challenged on Venus and Titan by their optically-thick atmospheres. Microwave radiometry in principle offers the ability to detect emission from surface thermal anomalies on these worlds due to greater atmospheric transparency: microwaves also offer the prospect of sensing the shallow subsurface and thus may detect warmth from lava flows for longer than surface infrared emission. However, satellite microwave instruments typically have low spatial resolution (10s of km) so volcanic heat is diluted in the wide instrument footprint. We examine the prospects for the detection of volcanic deposits by microwave, given likely planetary eruption rates and lava flow deposit geometries, using Mt Etna as a template. Nondetection of prominent hotspots in Cassini data may imply that the resurfacing rate is lower than ∼2 km3/yr, five times smaller than the expression of an Earth-like fraction of geothermal heat flow as latent heat in extrusive volcanism.

Ceres has a Thin, Hazy Atmosphere, Salty Craters, (probably) Cryovolcanoes and (possibly) Originated out by Pluto

The verdict is in — mostly. The bright spots on the dwarf planet Ceres are probably made of salt, NASA’s Dawn spacecraft has found.

Mixed with the salt are bits of rock and frozen water. When sunlight hits the blend, the ice sublimates into a misty haze above two of Ceres’s craters, researchers report in the 10 December issue of Nature.

But mission scientists are not sure how the salt, ice and haze are interlinked. “The whole picture we do not have yet,” says Andreas Nathues, a planetary scientist at the Max Planck Institute for Solar System Research in Goettingen, Germany, and the paper’s lead author1.

Dawn has also found ammonia-rich clays on Ceres, a second Nature paper reports2. Ammonia is more common in the frigid outer Solar System than in the asteroid belt where Ceres reigns. The discovery suggests that Ceres may have collected bits of outer Solar System material — or even that it was born near Neptune before migrating inward.

Both papers are the first major published results from Dawn. The spacecraft, which launched in 2007, visited the asteroid Vesta in 2011–12 and arrived at Ceres in March.

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New Exciting Results From Pluto

1. There are two icy calderas near Pluto's south pole.  These would be the first ice volcanoes seen.
2. The mountains on Pluto appear to mimic icebergs rather than mountains on Earth.
3. Pluto, too, seems to have a subterranean ocean.
4. Pluto's atmosphere is completely different than we anticipated, including hydrogen cyanide. 
5. Pluto's lesser Moons are very different than expected.  There appear to have been another two more moons in the past.

link.

Enceladus' Plumes are 1/6th the Mass Previously Thought

Aggregate particles in the plumes of Enceladus

Authors:

Gao et al

Abstract:

Estimates of the total particulate mass of the plumes of Enceladus are important to constrain theories of particle formation and transport at the surface and interior of the satellite. We revisit the calculations of Ingersoll and Ewald (Ingersoll, A.P., Ewald, S.P. [2011]. Icarus 216(2), 492–506), who estimated the particulate mass of the Enceladus plumes from strongly forward scattered light in Cassini ISS images. We model the plume as a combination of spherical particles and irregular aggregates resulting from the coagulation of spherical monomers, the latter of which allows for plumes of lower particulate mass. Though a continuum of solutions are permitted by the model, the best fits to the ISS data consist either of low mass plumes composed entirely of small aggregates or high mass plumes composed of mostly spheres. The high particulate mass plumes have total particulate masses of (166 ± 42) × 103 kg, consistent with the results of Ingersoll and Ewald (Ingersoll, A.P., Ewald, S.P. [2011]. Icarus 216(2), 492–506). The low particulate mass plumes have masses of (25 ± 4) × 103 kg, leading to a solid to vapor mass ratio of 0.07 ± 0.01 for the plume. If indeed the plumes are made of such aggregates, then a vapor-based origin for the plume particles cannot be ruled out. Finally, we show that the residence time of the monomers inside the plume vents is sufficiently long for Brownian coagulation to form the aggregates before they are ejected to space.

Explaining the Plume Differences Between Europa and Enceladus

Linking Europa's plume activity to tides, tectonics, and liquid water

Authors:

Rhoden et al

Abstract:

Much of the geologic activity preserved on Europa's icy surface has been attributed to tidal deformation, mainly due to Europa's eccentric orbit. Although the surface is geologically young (30 - 80 Myr), there is little information as to whether tidally-driven surface processes are ongoing. However, a recent detection of water vapor near Europa's south pole suggests that it may be geologically active. Initial observations indicated that Europa's plume eruptions are time-variable and may be linked to its tidal cycle. Saturn's moon, Enceladus, which shares many similar traits with Europa, displays tidally-modulated plume eruptions, which bolstered this interpretation. However, additional observations of Europa at the same time in its orbit failed to yield a plume detection, casting doubt on the tidal control hypothesis. The purpose of this study is to analyze the timing of plume eruptions within the context of Europa's tidal cycle to determine whether such a link exists and examine the inferred similarities and differences between plume activity on Europa and Enceladus.

Do Orcus and Quaoar Have Liquid Cores?

Conditions for liquid or icy core existence in KBO objects: numerical simulations for Orcus and Quaoar

Authors:

Shchuko et al

Abstract:

In this article, we present a model describing the thermal evolution and structure of Kuiper Belt objects (KBO) as a function of the intensity of radiogenic heat sources, mean density and the object's formation time. We have studied numerically the dependence of the interior composition and structure of a forming body on the accretion rate and radionuclide content in the dust particles, as well as the impact of the radiogenic heat generation rate on the water phase transition dynamics. The model is applied to predict the present internal structure of Plutino (90482) Orcus and KBO (50000) Quaoar with special emphasis on the possibility of cryovolcanism.

Ceres may Have Cryovolcanism

Localized sources of water vapour on the dwarf planet (1) Ceres

Authors:

Küppers et al

Abstract:

The ‘snowline’ conventionally divides Solar System objects into dry bodies, ranging out to the main asteroid belt, and icy bodies beyond the belt. Models suggest that some of the icy bodies may have migrated into the asteroid belt1. Recent observations indicate the presence of water ice on the surface of some asteroids with sublimation a potential reason for the dust activity observed on others. Hydrated minerals have been found on the surface of the largest object in the asteroid belt, the dwarf planet (1) Ceres, which is thought to be differentiated into a silicate core with an icy mantle. The presence of water vapour around Ceres was suggested by a marginal detection of the photodissociation product of water, hydroxyl, but could not be confirmed by later, more sensitive observations. Here we report the detection of water vapour around Ceres, with at least 1026 molecules being produced per second, originating from localized sources that seem to be linked to mid-latitude regions on the surface. The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.

Titan Surface Brightness Changes Might be Evidence of Cryovolcanism

'Sotra Patera' and a possible equivalent on Earth, Kirishima volcano in Japan

Changes in surface brightness on Titan observed over four years by NASA’s Cassini spacecraft have added to evidence that cryovolcanism is active on Saturn’s largest Moon. Anezina Solomonidou has presented results at the European Planetary Science Congress (EPSC) 2013 in London.

The authors compared many volcanic-like features, such as flows, calderas and craters, with similar geological features found on the Earth to study the possibility of cryovolcanic activity within regions close to Titan’s equator.

Titan has an atmosphere rich in organic carbon-based compounds and has clouds and rains of liquid methane that mimic Earth’s water cycle. Its landscape is remarkably Earth-like with dunes and lakes, erosion due to weathering and tectonic-like features. Astronomers believe that beneath its icy surface there is an ocean of liquid water, possibly mixed with ammonia. The low number of impact craters seen on Titan suggests that the surface is relatively young and is therefore dynamic and active.

“All of these features, plus a need for a methane reservoir and volcanic activity to replenish the methane we have detected in the atmosphere, is compatible with the theory of active cryovolcanism on Titan,” said Solomonidou, of the Observatoire de Paris and National and Kapodistrian University of Athens.

Solomonidou and colleagues have investigated the potentially cryogenic regions of Tui Regio, Hotei Regio and Sotra Patera using Cassini’s Visual and Infrared Mapping Spectrometer (VIMS).

“We were able to penetrate the atmosphere with VIMS and view any changes in these surface features. Interestingly, the albedo (brightness) of two of the areas has changed with time,” explained Solomonidou. “Tui Regio got darker from 2005 to 2009 and Sotra Patera -- the most favorable cryovolcanic candidate on Titan -- got brighter between 2005 and 2006.”

Surface variations, together with spectral albedo properties and the presence of volcanic-like features, suggest that these cryovolcanic candidate regions are connected to Titan’s deep liquid ocean.

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The other thought is it might be "snow."