Water/Hycean Worlds & Oceanography

Atmospheric Carbon Depletion As A Tracer Of Water Oceans And Biomass On Temperate Terrestrial Exoplanets

By Keith Cowing
Status Report
October 24, 2023
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Atmospheric Carbon Depletion As A Tracer Of Water Oceans And Biomass On Temperate Terrestrial Exoplanets
Illustration of our strategy to detect habitable exoplanetary environment via CO2 depletion. Each of the planets to the right hand side of the star describes a different scenario discussed in the text (along with illustrative atmospheric concentrations). The panel on the left hand side depicts a simulation of the transmission spectrum of the temperate terrestrial planet TRAPPIST-1 f. We explore the detectability of an atmosphere with ∼ 10 JWST/NIRSpec Prism transit observations, the minimum needed to produce a reliable diagnostic. Note that the deviation from a flat signal (no atmosphere) is primarily supported by the strong absorption features of CO2, notably at 4.3 µm (highlighted). Exo-atmospheric models from 142 were used to make that panel. On the lower right hand side, we illustrate a simplified view of a carbon cycle involving surface liquid water and biology sequestering cycle and producing a depletion in atmospheric carbon. Atmospheric concentrations given near the planets are illustrative. astro-ph.EP

The conventional observables to identify a habitable or inhabited environment in exoplanets, such as an ocean glint or abundant atmospheric O2, will be challenging to detect with present or upcoming observatories.

Here we suggest a new signature. A low carbon abundance in the atmosphere of a temperate rocky planet, relative to other planets of the same system, traces the presence of substantial amount of liquid water, plate tectonic and/or biomass. We show that JWST can already perform such a search in some selected systems like TRAPPIST-1 via the CO2 band at 4.3μm, which falls in a spectral sweet spot where the overall noise budget and the effect of cloud/hazes are optimal.

We propose a 3-step strategy for transiting exoplanets: 1) detection of an atmosphere around temperate terrestrial planets in ∼10 transits for the most favorable systems, (2) assessment of atmospheric carbon depletion in ∼40 transits, (3) measurements of O3 abundance to disentangle between a water- vs biomass-supported carbon depletion in ∼100 transits.

The concept of carbon depletion as a signature for habitability is also applicable for next-generation direct imaging telescopes.

Amaury H.M.J. Triaud, Julien de Wit, Frieder Klein, Martin Turbet, Benjamin V. Rackham, Prajwal Niraula, Ana Glidden, Oliver E. Jagoutz, Matej Pec, Janusz J. Petkowski, Sara Seager, Franck Selsis

Comments: 35 pages, 5 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.14987 [astro-ph.EP] (or arXiv:2310.14987v1 [astro-ph.EP] for this version)
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Submission history
From: Amaury Triaud
[v1] Mon, 23 Oct 2023 14:37:15 UTC (1,094 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻