HR: 10:20h
AN: P52A-01    [Abstracts]
TI: Geologically agnostic approaches to constraining the ice shell thickness of Europa.
AU: Chyba, C
EM: cchyba@princeton.edu
AF: Dept. of Astrophysical Sciences, Princeton University Peyton Hall, Princeton, NJ 08544, United States
AU: * Hand, K P
EM: kevin.hand@gmail.com
AF: Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Drive, Pasadena, CA 91109, United States
AB: Working from the Galileo magnetometer results, we have set new constraints on the ice shell thickness and salinity of the Europan ocean [1]. The induced magnetic field response of Europa to the time-varying component of the background Jovian magnetic field necessitates a near-perfect conducting layer within approximately 10 km of the surface, with an optimal fit of 4 km thickness. Achieving the empirically constrained amplitude response [2] requires near-saturation salt concentrations in an ocean beneath a thin (<10 km) ice shell. If the amplitude response is determined to be lower than A = 0.97 ± 0.02, e.g. in the range of A = 0.90, then the salt concentration can be lowered by nearly an order of magnitude or the ice shell thickness can be increased by a factor of a few. Continuing analysis of the magnetometer data indicates that the amplitude may indeed be lower than reported by Schilling et al. (2004), (Schilling, Khurana, pers. comm.). Geochemically, we find that achieving near-saturation with either magnesium sulfate or sodium chloride is implausible [3]. This contradicts early geochemical work for Europa [4] but is consistent with other more recent models [5]. Geochemical models can support a few to a few tens of grams of salt per kg of water, yielding ocean conductivities of ~0.5-6 S/m. For an induced amplitude response of A > 0.9, these geochemical constraints require the ice shell to be < 30 km thick. For higher values of A, or for lower values on salinity, the ice thickness must be decreased. The ~5-10 g salt per kg models of [5, 6] will not work unless the amplitude is < 0.9 or the ice shell is < 10 km thick. [1] Hand, K.P. & Chyba, C.F. (2007) Icarus. [2] Schilling et al., (2004) JGR. [3] Hand (2007) PhD Thesis. [4] Kargel et al., (2000) Icarus [5] Zolotov and Shock, (2001) JGR [6] Zolotov et al. (2006) LPSC.
DE: 0406 Astrobiology and extraterrestrial materials
DE: 0716 Cryobiology (0475)
DE: 5462 Polar regions
DE: 6218 Jovian satellites
DE: 8135 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8424)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting