Enceladus and Europa, icy moons of Saturn and Jupiter, respectively, are believed to be habitable with liquid water oceans and therefore are of interest for future life detection missions and mission concepts. With the limited data from missions to these moons, many studies have sought to better constrain these conditions. With these constraints, researchers have, based on modeling and experimental studies, hypothesized a number of possible metabolisms that could exist on Europa and Enceladus if these worlds host life. The most often hypothesized metabolisms are methanogenesis for Enceladus and methane oxidation/sulfate reduction on Europa. Here, we outline, review, and compare the best estimated conditions of each moon’s ocean. We then discuss the hypothetical metabolisms that have been suggested to be present on these moons, based on laboratory studies and Earth analogs. We also detail different detection methods that could be used to detect these hypothetical metabolic reactions and make recommendations for future research and considerations for future missions.
Carbon reduction is an important process for Earth-like origins of life events and of great interest to the astrobiology community. In this paper, we have collected experimental results, field work and modelling data on CO and CO2 reduction in order to summarize the research that has been carried out particularly in relation to the early Earth and Mars. By having a database of this work, researchers will be able to clearly survey the parameters tested and find knowledge gaps wherein more experimentation would be most beneficial. We focused on reviewing the modelling parameters, field work and laboratory conditions relevant to Mars and the early Earth. We highlight important areas addressed as well as suggest future work needed, including identifying relevant parameters to test in both laboratory and modelling work. We also discuss the utility of organizing research results in such a database in astrobiology.
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