Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p33b1573b&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P33B-1573
Mathematics
Logic
[0716] Cryosphere / Cryobiology, [4840] Oceanography: Biological And Chemical / Microbiology And Microbial Ecology, [5200] Planetary Sciences: Astrobiology, [5422] Planetary Sciences: Solid Surface Planets / Ices
Scientific paper
The science surrounding missions to the outer planets has been dominated by geophysical questions. The Europa Jupiter System Mission (EJSM), however, is a search explicitly for a “habitable world”. While not a life detection mission, the presence of ice penetrating radar (IPR) and other instruments provides an opportunity to answer questions that are biological in nature. The IPR will characterize the ice structure, including any subsurface water and ice-water interfaces. If life is to be found on Europa it may be present at the first water-ice interface; water lenses within the shell closer to the Europan surface than the ice-ocean interface. IPR can confirm the presence and abundance of these putative habitats, potentially within range of future life detection missions. EJSM will also directly inform biologists by determining some ice properties and estimating its rate of overturn, constraining the flux of oxidants and thus the amount of metabolism that can be supported. Terrestrial analogues may be useful models for the Europan ice-ocean system as revealed by IPR. The underside of sea ice represents a concentrated zone of life, defined by the availability of energy, along a column thousands of meters in length. For phototrophs attachment to the underside of sea ice guarantees access to light. For heterotrophs association ensures a supply of chemical energy in the form of organic carbon. If life exists on Europa we might expect a similar scenario, in this case with chemolithotrophs using the ice as a conduit for energy. This strategy suggests that if life is to be found on Europa it may well reach its highest concentration at the uppermost ice-water interface. Similarly, within saline ice biology is strongly associated with interstitial spaces: microscale channels and pores that result from the differential freezing of saline water. Within these spaces material is concentrated, providing an environment enriched in chemical energy. Here we present several habitat parameters that can be directly assessed via IPR, and discuss biological questions that EJSM may answer in the context of terrestrial analogues with an emphasis on multiyear sea ice (MYI). Although subglacial lakes may be analogues for a biosphere deep in the Europan ocean, MYI may share more structural similarities with the Europan ice shell than grounded glacial ice. Calculations suggest that organic and inorganic materials within the interstial spaces of MYI are concentrated as much as 500 fold, possibly aiding microbial metabolism through periods of very low temperature. In a similar manner organic carbon from endogenic or exogenic sources on Europa would concentrate in these spaces, serving as a valuable electron donor or acceptor for organisms in the ice. An environment’s physical structure helps structure the community which inhabits it, thus the MYI microbial community should inform a developing model of a hypothetical Europan ecosystem. Recent applications of 454 sequencing technology to the MYI community indicates a surprising degree of diversity within this environment, similar to that of underlying seawater. These findings suggest the potential for a diverse Europan microbial ecosystem despite energy limitations imposed by a permanent ice cover.
Bowman James S.
Schmidt Britney Elyce
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