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Open AccessArticle

Photosynthesis in Hydrogen-Dominated Atmospheres

by William Bains 1,3,*, Sara Seager 1,2 and Andras Zsom 1
1
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
2
Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
3
Rufus Scientific Ltd, 37 The Moor, Melbourn, Royston, Herts SG8 6ED, UK
*
Author to whom correspondence should be addressed.
Life 2014, 4(4), 716-744; https://doi.org/10.3390/life4040716
Received: 10 June 2014 / Revised: 11 October 2014 / Accepted: 13 October 2014 / Published: 18 November 2014
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
The diversity of extrasolar planets discovered in the last decade shows that we should not be constrained to look for life in environments similar to early or present-day Earth. Super-Earth exoplanets are being discovered with increasing frequency, and some will be able to retain a stable, hydrogen-dominated atmosphere. We explore the possibilities for photosynthesis on a rocky planet with a thin H2-dominated atmosphere. If a rocky, H2-dominated planet harbors life, then that life is likely to convert atmospheric carbon into methane. Outgassing may also build an atmosphere in which methane is the principal carbon species. We describe the possible chemical routes for photosynthesis starting from methane and show that less energy and lower energy photons could drive CH4-based photosynthesis as compared with CO2-based photosynthesis. We find that a by-product biosignature gas is likely to be H2, which is not distinct from the hydrogen already present in the environment. Ammonia is a potential biosignature gas of hydrogenic photosynthesis that is unlikely to be generated abiologically. We suggest that the evolution of methane-based photosynthesis is at least as likely as the evolution of anoxygenic photosynthesis on Earth and may support the evolution of complex life. View Full-Text
Keywords: photosynthesis; exoplanet; biomass; hydrogen atmosphere photosynthesis; exoplanet; biomass; hydrogen atmosphere
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Bains, W.; Seager, S.; Zsom, A. Photosynthesis in Hydrogen-Dominated Atmospheres. Life 2014, 4, 716-744.

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