HR: 1340h
AN: SA13A-1125    [Abstracts]
TI: Habitability in High Radiation Environments: The Case for Gaia at Europa
AU: * Cooper, J F
EM: jfcooper@pop600.gsfc.nasa.gov
AF: Raytheon Technical Services Company LLC, SSDOO Project, Code 632, NASA Goddard Space Flight Center, Greenbelt, MD 20771 United States
AB: In the paper of Cooper et al. (2001) we concluded, in relation to our work on magnetospheric irradiation of Europa and the other icy galilean moons of Jupiter, that 'icy satellites with significant heat, irradiation, and subsurface water resources may provide common abodes for life throughout the universe'. This expanded the original proposal of Chyba (2000) and his later works that radiolytic production of oxidants and simple hydrocarbons on Europa's icy surface could support evolution and survival of life within a Europan subsurface ocean. In the general case of icy planets and moons the radiation environment does not have to interact directly with the surface but could also provide energy for life through radiation-induced chemistry in thick atmospheres chemically coupled to icy surfaces with hydrocarbon reservoirs as on Titan. The Gaia model for Earth implies that the entire planet operates with atmospheric, geologic, and geochemical processes conducive to life. Essential requirements for Gaia are an oxidizing atmospheric environment at planetary surfaces, where oxidants like molecular oxygen are produced by radiation processes (mediated by photosynthetic chemistry on Earth but more directly produced by radiolysis on Europa), reservoirs of liquid water and hydrocarbons on or below the surface, other reduced materials in the interior, and geologic processes which drive chemical exchange between the chemically oxidized surface and reduced interior environments. At Europa a thin oxygen atmosphere is observed and arises from magnetospheric interaction, and there is much evidence for active resurfacing likely related to solid-state convection and diapiric processes within a thick crust of soft ice overlying a liquid ocean. These processes on Europa are analogous to that of the tectonic conveyer belt that continually recycles carbon, oxygen, and other essential materials for life between the atmosphere, surface, and interior on Earth. The ice crust at Europa could be thin and support more direct and rapid chemical exchange between the highly irradiated surface and the ocean, but this is not required for life since deep convection can accomplish the same exchange over thousands to millions of years. Hydrocarbons are likely present both from moon formation and later delivery to the surface by impacts of cometary bodies. More recent work from Galileo suggests strong associations between spatial distributions of brine-like materials on Europa's surface and geologic structures related to convection in the ice crust, tidal heating, and the underlying ocean. The effect of the brines on convection may be analogous to thermahaline circulation in the terrestrial oceans. The detected hydrated sulfates (including briny salts and sulfuric acid hydrates) on Europa's surface can at least in part be attributed to input of iogenic sulfur from the Jovian magnetosphere and radiolytic processing. The needed conveyer belt process within Europa could then be substantially driven by surface interaction with the magnetosphere, i.e. there could be radiation-driven geology, and this could make a critical contribution to astrobiological habitability within Europa. In the sense of Gaia and with reference to Edgar Allan Poe's famous work, Europa may have a tell-tale beating heart, and future missions such as the Jupiter icy Moons Orbiter (JIMO) will need to survive, look through, and exploit the local magnetospheric, ionospheric, and atmospheric environments to sense its physical, chemical, and electromagnetic presence. References: Cooper, J. F., et al., Icarus, 149, 133-159, 2001; Chyba, C. F., Nature, 403, 381, 2000.
DE: 6030 Magnetic fields and magnetism
DE: 6055 Surfaces and interiors
DE: 6218 Jovian satellites
DE: 2732 Magnetosphere interactions with satellites and rings
DE: 2756 Planetary magnetospheres (5443, 5737, 6030)
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting