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STScI Astrobiology Lecture Series

Life on Super-Earths

Presented by: William Bains (Massachusetts Institute of Technology - (Program in Atmospheres, Oceans and Climate))
Category: Science Colloquia   Duration: 2 hours and 30 minutes   Broadcast date: May 01, 2015
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Super-Earths are a class of planet not known in our Solar System but common among exoplanets. Can life survive there, and how would we detect it? I will present work exploring life on such worlds, especially Super-Earths with atmospheres that retain substantial amounts of hydrogen, and hence which will have surface chemistries substantially different from our own planet's. Surprisingly, the chemical inputs and outputs of life can be worked out from simple assumptions (or knowledge, when we have the knowledge) about planetary chemistry and environment, and the necessary properties of life. Some basic properties of the chemistry of life can be worked out from first principles: it must 'feed on' an energy source, it must be made of complex molecules which must therefore be of intermediate redox state. In the context of an hydrogen-rich super-Earth, I will discuss how these allow us to understand what biosignature gases such life could make. Gases can come from energy-generating reactions, and these are mostly constrained by the environment in which life grows. Gases can come from photosynthesis, which is also constrained by the environmental chemicals from which life builds its biomass. In both cases, we can not only identify the gases but also estimate the production rate, and hence whether it is plausible that life can make a detectable level of the gas. The third class of gases - those made by secondary metabolism - are harder to predict. Some modeling can be done, and I will touch on the issue of what chemicals to model. Lastly, I will mention the range of habitats, and hence of planetary environments, that such life might inhabit. Life on Super-Earth may actually be much more common than life on true Earth-analogues, but alas might also be much harder to detect.