Photosynthesis in Hydrogen-Dominated Atmospheres

Life

William Bains¹  Sara Seager¹  Andras Zsom¹  Dirk Schulze-Makuch² 

[1] Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA; E-Mails:Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA;

关键词: photosynthesis;    exoplanet;    biomass;    hydrogen atmosphere;   

DOI  :  10.3390/life4040716

来源: mdpi

【 摘 要 】

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.

【 授权许可】

CC BY   
© 2014 by the authors; licensee MDPI, Basel, Switzerland.