Por uma lista de moléculas como gases potenciais de assinatura na busca de vida em exoplanetas e aplicações na bioquímica terrestre

sexta-feira, maio 06, 2016

Toward a List of Molecules as Potential Biosignature Gases for the Search for Life on Exoplanets and Applications to Terrestrial Biochemistry

To cite this article:

Seager S., Bains W., and Petkowski J.J.. Astrobiology. April 2016, ahead of print. doi:10.1089/ast.2015.1404.

Online Ahead of Print: April 20, 2016

S. Seager,1,2 W. Bains,1,3 and J.J. Petkowski1

1Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts.

2Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts.

3Rufus Scientific, Cambridge, UK.

Address correspondence to:

S. Seager
Department of Earth, Atmospheric, and Planetary Sciences
Massachusetts Institute of Technology
54-1626 77 Massachusetts Ave.
Cambridge, MA 02139

E-mail: seager@mit.edu

Submitted 7 September 2015 Accepted 24 February 2016 


Thousands of exoplanets are known to orbit nearby stars. Plans for the next generation of space-based and ground-based telescopes are fueling the anticipation that a precious few habitable planets can be identified in the coming decade. Even more highly anticipated is the chance to find signs of life on these habitable planets by way of biosignature gases. But which gases should we search for? Although a few biosignature gases are prominent in Earth's atmospheric spectrum (O2, CH4, N2O), others have been considered as being produced at or able to accumulate to higher levels on exo-Earths (e.g., dimethyl sulfide and CH3Cl). Life on Earth produces thousands of different gases (although most in very small quantities). Some might be produced and/or accumulate in an exo-Earth atmosphere to high levels, depending on the exo-Earth ecology and surface and atmospheric chemistry.

To maximize our chances of recognizing biosignature gases, we promote the concept that all stable and potentially volatile molecules should initially be considered as viable biosignature gases. We present a new approach to the subject of biosignature gases by systematically constructing lists of volatile molecules in different categories. An exhaustive list up to six non-H atoms is presented, totaling about 14,000 molecules. About 2500 of these are CNOPSH compounds. An approach for extending the list to larger molecules is described. We further show that about one-fourth of CNOPSH molecules (again, up to N = 6 non-H atoms) are known to be produced by life on Earth. The list can be used to study classes of chemicals that might be potential biosignature gases, considering their accumulation and possible false positives on exoplanets with atmospheres and surface environments different from Earth's. The list can also be used for terrestrial biochemistry applications, some examples of which are provided. We provide an online community usage database to serve as a registry for volatile molecules including biogenic compounds. Key Words: Astrobiology—Atmospheric gases—Biosignatures—Exoplanets. Astrobiology 16, xxx–xxx.

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