Follow the Oxygen: Comparative Histories of Planetary Oxygenation and Opportunities for Aerobic Life
Abstract
Aerobic respiration—the reduction of molecular oxygen (O_2) coupled to the oxidation of reduced compounds such as organic carbon, ferrous iron, reduced sulfur compounds, or molecular hydrogen while conserving energy to drive cellular processes—is the most widespread and bioenergetically favorable metabolism on Earth today. Aerobic respiration is essential for the development of complex multicellular life; thus the presence of abundant O_2 is an important metric for planetary habitability. O_2 on Earth is supplied by oxygenic photosynthesis, but it is becoming more widely understood that abiotic processes may supply meaningful amounts of O_2 on other worlds. The modern atmosphere and rock record of Mars suggest a history of relatively high O2 as a result of photochemical processes, potentially overlapping with the range of O_2 concentrations used by biology. Europa may have accumulated high O_2 concentrations in its subsurface ocean due to the radiolysis of water ice at its surface. Recent modeling efforts suggest that coexisting water and O2 may be common on exoplanets, with confirmation from measurements of exoplanet atmospheres potentially coming soon. In all these cases, O_2 accumulates through abiotic processes—independent of water-oxidizing photosynthesis. We hypothesize that abiogenic O_2 may enhance the habitability of some planetary environments, allowing highly energetic aerobic respiration and potentially even the development of complex multicellular life which depends on it, without the need to first evolve oxygenic photosynthesis. This hypothesis is testable with further exploration and life-detection efforts on O_2-rich worlds such as Mars and Europa, and comparison to O_2-poor worlds such as Enceladus. This hypothesis further suggests a new dimension to planetary habitability: "Follow the Oxygen," in which environments with opportunities for energy-rich metabolisms such as aerobic respiration are preferentially targeted for investigation and life detection.
Additional Information
© 2019 Mary Ann Liebert, Inc., publishers. Submitted 13 July 2018; Accepted 7 January 2019; Published Online:7 Jun 2019. This work was performed in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. © 2018, California Institute of Technology. The authors would like to acknowledge funding support from the Simons Collaboration on the Origin of Life (V.S. and W.W.F.), a NASA NESSF fellowship to L.M.W. (NNX16AP39H), the Agouron institute (L.M.W. and W.W.F.), and a NASA Exobiology grant to W.W.F. (NNX16AJ57G). The authors would like to thank Norm Sleep and two anonymous reviewers for helpful comments that have improved the manuscript.Attached Files
Published - ast.2017.1779.pdf
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Additional details
- Eprint ID
- 96456
- Resolver ID
- CaltechAUTHORS:20190617-101021543
- Simons Collaboration on Origins of Life
- NASA Earth and Space Science Fellowship
- NNX16AP39H
- Agouron Institute
- NASA
- NNX16AJ57G
- NASA/JPL/Caltech
- Created
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2019-06-17Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field