炭素の少ない大気は、他の地球型惑星に水と生命が存在する兆候である可能性をMITの研究が発見(A carbon-lite atmosphere could be a sign of water and life on other terrestrial planets, MIT study finds)

2023-12-28 マサチューセッツ工科大学(MIT)

＜関連情報＞

• https://news.mit.edu/2023/carbon-lite-atmosphere-life-terrestrial-planets-mit-study-1228
• https://www.nature.com/articles/s41550-023-02157-9

太陽系外惑星の水海洋とバイオマスのトレーサーとしての大気中の炭素枯渇 Atmospheric carbon depletion as a tracer of water oceans and biomass on temperate terrestrial exoplanets

Amaury H. M. J. Triaud,Julien de Wit,Frieder Klein,Martin Turbet,Benjamin V. Rackham,Prajwal Niraula,Ana Glidden,Oliver E. Jagoutz,Matej Peč,Janusz J. Petkowski,Sara Seager & Franck Selsis
Nature Astronomy  Published:28 December 2023
DOI:https://doi.org/10.1038/s41550-023-02157-9

Abstract

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 a substantial amount of liquid water, plate tectonics and/or biomass. Here we show that JWST can already perform such a search in some selected systems such as TRAPPIST-1 via the CO₂ band at 4.3 μm, which falls in a spectral sweet spot where the overall noise budget and the effect of cloud and/or hazes are optimal. We propose a three-step strategy for transiting exoplanets: detection of an atmosphere around temperate terrestrial planets in about 10 transits for the most favourable systems; assessment of atmospheric carbon depletion in about 40 transits; and measurements of O₃ abundance to disentangle between a water- versus biomass-supported carbon depletion in about 100 transits. The concept of carbon depletion as a signature for habitability is also applicable for next-generation direct-imaging telescopes.