On the habitability of Europa

It has recently been suggested that tidal and radiogenic heating of Europa has led to formation and maintenance of a liquid water ocean overlain by a thin ice crust ( S. W. Squyres, R. T. Reynolds, P. M. Cassen, and S. J. Peale (1983). Nature 301, 225–226 ). The present work examines the environmental consequences of such a model with regard to the possible existence on Europa of regions that could satisfy the basic requirements for the survival of known organisms. Appropriate temperatures and long-term environmental stability are implied by the ocean model. The presence of necessary biogenic elements is assumed based on the expected origin of the ocean. The availability of biologically useful energy is assumed to be the principal limiting factor for life on Europa. Possible electrical, thermal, and chemical energy sources are discussed. Calculated resurfacing rates for the active crust model are used to estimate the quantity of photosynthetically active radiation that might reach the proposed ocean through crustal fractures. The amount of biomass that this energy could support, based on Antartic microorganism analogs, is estimated and discussed. Although these calculations cannot determine whether life forms exist or could exist on Europa, they do suggest that there may be regions on Europa, very limited on both space and time, with physical conditions that are within the range of adaptation of life on Earth.