HR: 0830h
AN: P51B-0452    [PDF]
TI: Clathrate Hydrates in a Europan Ocean
AU: * Hand, K P
EM: khand@pangea.stanford.edu
AF: Department of Geological and Evnironmental Sciences, Stanford University, Bldg. 320, Geocorner, Stanford, CA 94305 United States
AU: Chyba, C F
EM: chyba@seti.org
AF: Department of Geological and Evnironmental Sciences, Stanford University, Bldg. 320, Geocorner, Stanford, CA 94305 United States
AU: Chyba, C F
EM: chyba@seti.org
AF: Center for the Study of Life in the Universe, SETI Institute, 2035 Landings Drive, Mountain View, CA 94043 United States
AB: The temperature and pressure environments of the europan ice shell and putative ocean may be such that various species of clathrate hydrates are stable. Here we calculate annual fluxes of biologically useful gases to a europan ocean and consider the role of such clathrates in a hypothetical europan ecosystem. It is known that the surface radiation environment of Europa produces O$_{2}$, hydrogen peroxide, and H$_{2}$S(Carlson et al., 1999) Thus, hydrates of these species could form in the ice shell or in the ocean if conditions were suitable. According to Lipenkov \& Istomin, if pressures in the ice shell exceeded ~9.7 MPa for temperatures $>$267 K then oxygen hydrates would form in the ice. Such conditions might be expected at the base of the ice shell or in regions of high tidal stress or strain. If we make the assumption that the solubility of oxygen in Europa is comparable to that calculated for Lake Vostok temperatures and pressures, then we can estimate the extent to which the europan ocean might contain dissolved oxygen and hydrates. Taking an estimate based on radiolytic surface production of hydrogen peroxide (which decays to oxygen) and subsequent delivery to the ocean, we have argued that Europa could have an annual oxygen flux of 10$^{12}$ moles. Over the course of the ~50 million year resurfacing timescale, this would produce a ~0.020 mole fraction of oxygen in the ocean, in the absence of oxygen sinks (Chyba \& Hand, 2001). By comparison with Lipenkov and Istomin, this exceeds the 2.2e-3 maximum solubility for air and thus in this case we would expect to see oxygen hydrate formation in the Europan ocean. Several caveats apply: 1) We have in this estimate used the solubility for air, not pure oxygen; 2) The gases delivered to the ocean would be at ~10MPa and 272 K, this is not a high enough pressure for oxygen hydrate stability, however if the pressure were to reach levels of 11-12MPa then such hydrates would be stable. Once delivered to the ocean, the fate of biologically useful gas hydrates will depend on the density, and hence salinity, of the europan ocean water. If the density of the hydrates exceeds that of the surrounding water and saturation has been reached, then the hydrates will precipitate to the seafloor and form a hydrate sediment. If the hydrates are buoyant in the europan ocean then an accretion layer of hydrates may form at the base of the ice shell. Indeed, such a layer may have implications for ice shell dynamics and evolution.
DE: 0400 Biogeosciences
DE: 6207 Comparative planetology
DE: 6218 Jovian satellites
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting