Astrobiological Aspects of Radiation Chemistry in Europa's Icy Regolith

Details Astrobiological Aspects of Radiation Chemistry in Europa's Icy Regolith Astrobiological Aspects of Radiation Chemistry in Europa's Icy Regolith

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.p23a..01c&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P23A-01

Biology

Quantitative Biology

Biomolecules

6020 Ices, 6060 Radiation And Chemistry, 6221 Europa, 0424 Biosignatures And Proxies

Scientific paper

Jupiter's moon Europa, with its likely subsurface ocean and young, active surface, is a promising habitat for life. Europa orbits in the heart of Jupiter's powerful magnetosphere and suffers intense energetic particle bombardment, producing both positive and negative aspects for astrobiology at Europa. Ionizing radiation can produce oxidants that could support a radiation-driven ecology as proposed by Chyba. On the other hand, biomolecular evidence for life that may be upwelled to the surface is rapidly altered by irradiation, complicating astrobiological searches for evidence of life. We present an overview of laboratory work performed at JPL and elsewhere and observational results related to these two aspects. The oxidants hydrogen peroxide and molecular oxygen are known to exist on Europa and the radiolytic production of these species has been studied in the laboratory for both electron and ion irradiation. Laboratory- measured equilibrium concentrations of H2O2, where production and destruction rates are equal, are in general agreement with the observed 0.1% molar abundance on Europa. The shape of Europa's peroxide band is consistent with the line shapes observed in radiolysis and with H2O2 dispersed in water ice rather than occurring as H2O2 aggregates. Surprisingly, molecular oxygen may be even more abundant on Europa even though O2 is extremely volatile ande would be expected to escape from the ice surface. Radiolysis can produce molecular oxygen and appears to simultaneously alter the ice matrix, trapping the O2. Other species observed on Europa are CO2 and SO2, and laboratory radiolysis of these species in H2O ice produces carbonic and sulfuric acid, respectively. We are studying the radiolytic degradation of biomarkers in ice at Europa temperatures by studying both simple organics and more complex biomolecules, including microorganisms. Hydrocarbon radiolysis yields carbon dioxide and methane, which can escape the system and results in loss of carbon. In addition, polymerization produces brown, high-molecular weight residues with complex mass spectra. Radiolysis of microorganisms shows the loss of amine, amide, methyl, and methylene groups, and production of carbon dioxide, carbon monoxide, nitriles, and isocyanates. Work is continuing to establish useful biosignatures that may persist in the complex mass spectra of irradiated microorganisms.

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