Testing for evolutionary trends of Europan biota

摘要

The present work was stimulated by the possibility of designing an advanced lander mission that may melt through the ice layer above the Europan ocean, in order to deploy a tethered submersible. We devote our attention to the determination of the degree of evolution of the biota, and the determination of the Europan environments that should be probed. As the most likely microorganisms in the Europa ocean are archaebacteria, we argue that evolution should have occurred, as hydrothermal vents are assumed to be present at the bottom of the ocean and such environments are known not to be refuges against evolution. We argue that a factor in interpreting the lack of uniformity in surface brightness and color of the Europan surface may be the presence of microorganisms. This hypothesis can be tested by spectroscopic search for not only the precursors of biomolecules (as has already been confirmed by the Galileo Mission in the case of Ganymede and Callisto), but a spectroscopic search should also be conducted for the biomolecules themselves, such as nucleotides, aminoacids, lipids and polysaccharides. The submersible seems to be the most appropriate means for a program in the search for extraterrestrial eukaryotes (SETE), but we also discuss SETE in the context of another proposal.