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Kevin Hand

Scientist
Jet Propulsion Laboratory
4800 Oak Grove Drive M/S 183-601
Pasadena, CA 91109

1. Habitability of icy worlds
2. Magnetic field interactions
3. Laboratory experiments of radiolytic chemistry
4. Life detection
5. Astrobiology

Title 1: Magnetic Field Interactions at Europa

Abstract 1:

This talk details numerical and laboratory investigations of jovian magnetic field interactions with Europa. Results from the Galileio spacecraft magnetometer were used to investigate the sub-surface ocean chemistry of Europa and to derive relationships for salinity and ice layer thickness as a function of induced amplitude response. The physics of this interaction is presented in detail at a level appropriate for advanced undergraduates. The best fit of our model to the currently available data is a 4 km ice shell and near-saturation salt concentrations. These results hold for both a 3-layer spherical model (mantle-ocean-ice) and a 5-layer half space model (adding an ionosphere and core). This is the first empirical constraint provided for the ice shell thickness independent of surface geology and thermal models.

In addition to the numerical modeling described above, the effect of the jovian magnetic field on the surface ice of Europa was investigated experimentally. A cryostat-coupled vacuum chamber with a high-energy electron gun was used to irradiate thin ice films at temperatures (70-120 K) and pressures 10^-9 torr appropriate to Europa. Hydrogen peroxide production was measured for a range of temperatures, beam currents, and electron energies. When combined with a mathematical model for total H2O2 production and destruction over the range of incident electrons energies (~0.1-10^-4 keV) it was found that sub-surface H2O2 concentrations could be significantly larger than the observed surface abundance (several percent versus 0.13% by number relative to water).

Ice mixtures of H2O and various combinations of CO2, propane, propene, butane, (1-,2-)butene, and ammonia were irradiated to examine the resulting organic chemistry and possible prebiotic chemistry. Clathrate hydrates were considered as mechanism for trapping volatile species and numerical models combined with laboratory results suport this hypothesis. Calculations for oxidant delivery to the sub-surface ocean show that Europa's ocean is not likely to be oxidant limited. Finally, the chemistry resulting from surface radiolysis is discussed in the context of habitability.

Title 2: Searching for a Second Origin: Understanding the physics and chemistry of the ocean of Europa, with an eye toward biology.

Abstract 2:

Europa, Jupiter's second large moon, almost certainly harbors a global sub-surface ocean containing 2-3 times the volume of all the liquid water on Earth. This ocean has likely persisted for the history of the solar system and as such it presents a compelling world in our search for life beyond Earth. Furthermore, due to the factors of distance, radiation, and a thick ice shell, Europa is unlikely to have been seeded by life from Earth or Mars. If life were to be found on Europa, it would likely represent a second, independent origin of life in our solar system and it would allow us to investigate the uniqueness of our own DNA, RNA, and protein-based biochemistry. Here I present results of numerical models and laboratory investigations of the interaction of the jovian magnetic field with Europa. It is largely through this interaction that we have knowledge of the sub-surface ocean. Results from the Galileo spacecraft magnetometer were used to investigate the sub-surface ocean chemistry and to derive relationships for salinity and ice layer thickness as a function of the amplitude of the induced magnetic field. The best fit to the currently available data was found to be a 4 km ice shell and near-saturation salt concentrations in the ocean. Interestingly, results for salt concentration imply that contemporary Europa could be suitable for terrestrial halophilic organisms, but it may be too salty to allow for the origin of life as we know it.

Energetic particles (protons, electrons, and ions) within the magnetic field of Jupiter bombard the surface ice of Europa, creating a surface rich in oxygen, hydrogen peroxide, and sulfate. If these compounds are delivered to the ocean they could serve to maintain an ocean rich in chemical energy useful for life. Calculations for oxidant delivery to the sub-surface ocean - accounting for consumption by geologically produced reductants - show that Europa's ocean is not likely to be oxidant limited. Were biology to be present, the chemical energy available through delivery of radiolytically produced surface oxidants could be great enough to support organisms comparable to terrestrial ocean macrofauna.

Finally, an inhabited world is of little interest if its inhabitants cannot be detected. With this in mind I will address the issue of biomarkers on the surface of Europa and the prospect of detecting such biomarkers using an orbiting spacecraft. This work will help guide us as NASA prepares for the Europa Explorer mission, hopefully to be launched in the next decade.