Is the Presence of Oxygen on an Exoplanet a Reliable Biosignature?

Details Is the Presence of Oxygen on an Exoplanet a Reliable Biosignature? Is the Presence of Oxygen on an Exoplanet a Reliable Biosignature?

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011asbio..11..335l&link_type=abstract

Astrobiology, Volume 11, Issue 4, pp. 335-341.

Biology

Biosignature, Oxygen, Ozone, Photosynthesis, Artificial Photosynthesis, Photocatalysis

Scientific paper

We revisit the validity of the presence of O2 or O3 in the atmosphere of a rocky planet as being a biosignature. Up to now, the false positive that has been identified applies to a planet during a hot greenhouse runaway, which is restricted to planets outside the habitable zone (HZ) of the star that are closer to the star. In this paper, we explore a new possibility based on abiotic photogeneration of O2 at the surface of a planet that could occur inside the HZ. The search for such a process is an active field of laboratory investigation that has resulted from an ongoing interest in finding efficient systems with the capacity to harvest solar energy on Earth. Although such a process is energetically viable, we find it to be a very unlikely explanation for the observation of O2 or O3 in the atmosphere of a telluric exoplanet in the HZ. It requires an efficient photocatalyst to be present and abundant under natural planetary conditions, which appears unlikely according to our discussion of known mineral photochemical processes. In contrast, a biological system that synthesizes its constituents from abundant raw materials and energy has the inherent adaptation advantage to become widespread and dominant (Darwinist argument). Thus, O2 appears to continue to be a good biosignature.

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