Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmmr54a..01s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #MR54A-01
Mathematics
Logic
3612 Reactions And Phase Equilibria (1012, 8412), 5422 Ices, 6063 Volcanism (5480, 8450), 8147 Planetary Interiors (5430, 5724, 6024)
Scientific paper
Volcanism on an Earth-like rocky planet is the result of partial melting during its thermal evolution. It provides unique information on the internal composition, dynamics and evolution of the planet. For example, the volcanism at mid-ocean ridges and hot spots on Earth is the surface evidence of mantle convection. The partial melt that occurs at depth (a few tens of kilometers) is lighter than the surrounding mantle and the overpressure leads to extrusions of the melt which eventually carries some mantle rocks to the surface. Because the mantle rock is formed of different minerals with different melting temperatures, the partial melting of the mantle leads to the formation of an oceanic crust that has, to first order, the composition of the mineral with the lowest melting temperature. Similarly, cryovolcanism on the icy moons of the outer planets provides unique information on their internal structure and dynamics. The observation of an active plume on the small moon Enceladus is a major discovery of the Cassini mission. The heat necessary to melt and vaporize the icy compounds is provided by the strong tides during Enceladus' eccentric orbit around Saturn. Different models have been invoked in order to explain the 4-8 GW of thermal emission at the South Pole area. Shear heating along the "tiger stripes" has been proposed to explain the energy released in the South Pole area and the cryovolcanism along the faults [Nimmo et al., Nature, 2007]. The presence of a liquid layer between the ice crust and the silicate core also leads to a large production of tidal heating in the ice crust [Tobie et al., Icarus, 2008]. This model also explains the long-lived presence of a liquid layer at depth. The plume is composed of 91% of H2O, 3% of CO2, 4% of N2 , and 2% CH4 [Waite et al., Science, 2008]. This composition suggests interaction between silicates and water with formation of methane by serpentinization of silicates accompanied by the formation of methane at the expense of CO or CO2 [Matson et al., Icarus, 2007]. On Titan, the SAR (Synthetic Aperture Radar) and the VIMS (Visual and Infrared Mapping Spectrometer) images suggest that several morphological features could be formed by cryovolcanic activity [Sotin et al., Nature, 2005; Barnes et al., GRL, 2006; Lopes et al., Icarus, 2007]. Such volcanism would explain the recent release of methane and its presence in the atmosphere where its lifetime is a few tens of millions of years. In order to link thermal evolution models and cryovolcanic models, it is necessary to have laboratory data that describe the melting temperature of different kinds of ices including clathrate hydrates containing ammonia, methane, nitrogen and other volatiles. Since the melting temperature of ammonia is small compared to that of water ice, it is a good candidate for explaining flow features seen on Titan's surface. However, the presence of an ocean at depth makes unlikely the presence of ammonia in the icy crust. More sophisticated models must be found with species such as methane and CO2. This work has been carried out at the JPL, Caltech, under contract with NASA.
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