Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p22a..02k&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P22A-02
Other
[5410] Planetary Sciences: Solid Surface Planets / Composition, [5418] Planetary Sciences: Solid Surface Planets / Heat Flow, [5460] Planetary Sciences: Solid Surface Planets / Physical Properties Of Materials, [5480] Planetary Sciences: Solid Surface Planets / Volcanism
Scientific paper
Almost as soon as low-temperature solar nebula condensation sequences were first computed, it was realized that icy satellites have an internal heat source in long-lived radioactivities and could undergo differentiation; furthermore, freezing-point depressants, such as ammonia, and apolar gases, such as methane, could enable icy satellites to undergo aqueous cryovolcanism. The subsequent recognition of tidal and gravitational potential energy sources increased expectations for cryovolcanism. Voyager imaging and discovery of apparent cryovolcanic landforms—best exhibited by Triton, more ambiguous elsewhere-- motivated studies of the phase relations, phase densities and other thermodynamic properties, solid- and liquid-state rheologies, and possible cryovolcanic eruptive behaviors and landform characteristics. Ironically, the closer we examined Jovian icy moons with Galileo, the rarer cryovolcanic landforms appeared to be, with only a few compelling and very well characterized cases found mainly on Europa. Compelling examples of effusive cryovolcanism mainly occupied local topographic lows, whereas cases not in low spots tended to exhibit signs of explosive emplacement. Spectacular evidence of explosive cryovolcanism or geyser-like behavior was found by Cassini on Enceladus, but most other icy Saturnian moons did not reveal any compelling indicators of eruptions. Titan has so far been a mixed case, where some indicators of cryovolcanism have been reported, but there is scant compelling evidence for the process. We think that the sparseness of compelling effusive cryovolcanic features on icy satellites is because free, unreacted ammonia is less common than previously thought, and the main aqueous liquids are salt-water solutions denser than ice I; hence, they tend not to erupt, or they erupt only if driven by gas exsolution; even then, a thin ice shell and high heat flow is needed to allow aqueous liquids near enough to the surface to erupt. On satellites with thick icy shells, stable aqueous liquids are mainly confined to deep levels and cryovolcanism does not occur unless ammonia is abundant, as it may be on Triton. On Titan, we think the icy shell is thick, ammonia might not be abundant, and aqueous cryovolcanism might occur rarely, if at all. However, many hydrocarbons are abundant on Titan—both photolytic and endogenic—and may melt in the icy crust and form low-temperature, buoyant liquids. Hydrocarbon cryovolcanism is likely. Hydrocarbon lavas may range from exceeding low viscosity unimolecular types to highly viscous and possibly asphalt-, wax-, or plastic-like solid-liquid mixtures of complex and highly polymerized compositions. Some hydrocarbons may melt just hundreds of meters to a few kilometers beneath Titan’s surface. Shallow hydrocarbon deposits may melt or crystallize when insulating surface hydrocarbon deposits are emplaced or removed by sublimation, fluvial, or eolian processes. Deep interior endogenic hydrocarbons may erupt if they evade a gauntlet of physical and chemical barriers during ascent. Hydrocarbon cryovolcanic landforms may resemble skating ponds, silicate lava flows, salt extrusions, asphalt flows, or glaciers.
Candelaria Pat
Furfaro Roberto
Kargel Jeff S.
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