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Glidden A, Seager S, Petkowski JJ, Ono S. Can Isotopologues Be Used as Biosignature Gases in Exoplanet Atmospheres? Life (Basel) 2023; 13:2325. [PMID: 38137926 PMCID: PMC10744769 DOI: 10.3390/life13122325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 10/25/2023] [Accepted: 11/15/2023] [Indexed: 12/24/2023] Open
Abstract
Isotopologue ratios are anticipated to be one of the most promising signs of life that can be observed remotely. On Earth, carbon isotopes have been used for decades as evidence of modern and early metabolic processes. In fact, carbon isotopes may be the oldest evidence for life on Earth, though there are alternative geological processes that can lead to the same magnitude of fractionation. However, using isotopologues as biosignature gases in exoplanet atmospheres presents several challenges. Most significantly, we will only have limited knowledge of the underlying abiotic carbon reservoir of an exoplanet. Atmospheric carbon isotope ratios will thus have to be compared against the local interstellar medium or, better yet, their host star. A further substantial complication is the limited precision of remote atmospheric measurements using spectroscopy. The various metabolic processes that cause isotope fractionation cause less fractionation than anticipated measurement precision (biological fractionation is typically 2 to 7%). While this level of precision is easily reachable in the laboratory or with special in situ instruments, it is out of reach of current telescope technology to measure isotope ratios for terrestrial exoplanet atmospheres. Thus, gas isotopologues are poor biosignatures for exoplanets given our current and foreseeable technological limitations.
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Affiliation(s)
- Ana Glidden
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Sara Seager
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Janusz J. Petkowski
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- JJ Scientific, Mazowieckie, 02-792 Warsaw, Poland
- Faculty of Environmental Engineering, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland
| | - Shuhei Ono
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Zhang Y, Snellen IAG, Bohn AJ, Mollière P, Ginski C, Hoeijmakers HJ, Kenworthy MA, Mamajek EE, Meshkat T, Reggiani M, Snik F. The 13CO-rich atmosphere of a young accreting super-Jupiter. Nature 2021; 595:370-372. [PMID: 34262209 DOI: 10.1038/s41586-021-03616-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 05/05/2021] [Indexed: 11/09/2022]
Abstract
Isotope abundance ratios have an important role in astronomy and planetary sciences, providing insights into the origin and evolution of the Solar System, interstellar chemistry and stellar nucleosynthesis1,2. In contrast to deuterium/hydrogen ratios, carbon isotope ratios are found to be roughly constant (around 89) in the Solar System1,3, but do vary on galactic scales with a 12C/13C isotopologue ratio of around 68 in the current local interstellar medium4-6. In molecular clouds and protoplanetary disks, 12CO/13CO ratios can be altered by ice and gas partitioning7, low-temperature isotopic ion-exchange reactions8 and isotope-selective photodissociation9. Here we report observations of 13CO in the atmosphere of the young, accreting super-Jupiter TYC 8998-760-1 b, at a statistical significance of more than six sigma. Marginalizing over the planet's atmospheric temperature structure, chemical composition and spectral calibration uncertainties suggests a 12CO/13CO ratio of [Formula: see text](90% confidence), a substantial enrichment in 13C with respect to the terrestrial standard and the local interstellar value. As the current location of TYC 8998-760-1 b at greater than or equal to 160 astronomical units is far beyond the CO snowline, we postulate that it accreted a substantial fraction of its carbon from ices enriched in 13C through fractionation.
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Affiliation(s)
- Yapeng Zhang
- Leiden Observatory, Leiden University, Leiden, The Netherlands
| | | | | | - Paul Mollière
- Max-Planck-Institut für Astronomie, Heidelberg, Germany
| | - Christian Ginski
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands
| | - H Jens Hoeijmakers
- Observatoire de Genève, Université de Genève, Versoix, Switzerland.,Lund Observatory, Department of Astronomy and Theoretical Physics, Lunds Universitet, Lund, Sweden
| | | | - Eric E Mamajek
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.,Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA
| | | | | | - Frans Snik
- Leiden Observatory, Leiden University, Leiden, The Netherlands
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