A Search for Extraterrestrial Eukaryotes: Biological and Planetary Science Aspects

摘要

Abstract One pressing question in bioastronomy is to attempt to devise assays in the search for extraterrestrial eukaryotes (SETE). In the positive case of encountering a fossil of a certain microorganism, it is not yet clear how to identify it in an unequivocal manner, even if found arrested and preserved in the midst of biological activity, as in some known Archean sediments on Earth. On the other hand, for living microorganisms the present approach may have some advantages over the straightforward probe of the morphological features of the putative eukaryote, as we argue that we are not constrained to base identification on morphological properties, such as the presence of organelles, which are known to be missing in some higher taxa. We sketch a possible experimental set-up required for a robot to investigate whether eukaryogenesis has already taken place in Mars or Europa. Besides, we also discuss the biological and astronomical implications of a SETE program. Previous observation and theoretical work have suggested that underneath the ice crust of the Jovian satellite Europa there may be an ocean of liquid water. We therefore argue that as hot springs may be present at the bottom of that ocean, eukaryotes should be searched for, not only deep in the Martian permafrost, as discussed by others, but a SETE program should be extended to the aquatic environment of the Jovian satellite as well. Our current work emphasising gene silencing, may suggest how to decide on the degree evolution which microbiota may have reached in the Europa ocean, a topic which deserves our attention, as eukaryogenesis is the process which introduced the basic cellular plan of those Earth-bound organisms that have been raised to the level of intelligent beings. We make a specific suggestion for a robotic investigation of eukaryogenesis in solar system exploration.