The Goldilocks Problem for Detecting Water in Terrestrial Planets: Constraining Water Abundances in the Mid-infrared with LIFE

The Astrophysical Journal, vol. 1003, pp. 85

Abstract

Abstract We investigate how well the Large Interferometer for Exoplanets (LIFE) mission concept can detect habitable conditions on exoplanets through the presence of atmospheric water vapor as a proxy for surface oceans. We model the atmosphere of a prebiotic Earth-like planet across a range of water concentrations, from water-poor to water-rich, with surface partial pressures from 10 −7 to 1 bar of H 2 O. We simulate LIFE-like noise at spectral resolutions R = 50 and 100 using LIFE sim and perform Bayesian atmospheric retrievals to determine the technical requirements for LIFE to confirm habitability. We model three vertical water distributions—a vertically constant profile, a Manabe–Wetherald-based Earth-like profile, and a diffusion and photochemistry profile—to test how the assumed vertical structure influences the retrieved abundances. Clouds are not modeled. We find the ability for LIFE to detect water strongly depends on the vertical profile assumed. LIFE is unable to constrain the highest-water cases and provides upper limits on low-water planets. For the highest-water abundances, absorption features saturate and reduce the sensitivity for characterizing precise H 2 O levels. Water vapor is not detectable in any profile modeled for ≤10 −6 bar in surface water, comparable to Mars. For an Earth-like profile, LIFE could constrain H 2 O concentrations from ∼10 −3 to 1 bar, spanning below and above present-day Earth concentrations of 10 −2 bar. Detectable atmospheric water may imply surface oceans, as water is highly reactive and rapidly removed by surface mineral reactions. Thus, LIFE can characterize water abundances indicative of habitable surface conditions.

Authors 9

1. Sarah Rugheimer

   York University · University of Edinburgh

   Affiliation as printed

   University of Edinburgh, Blackford Hill

   York University

2. Eleonora Alei

   Goddard Space Flight Center · Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Institute for Particle Physics & Astrophysics

   NASA Goddard Space Flight Center

3. Björn S. Konrad

   Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Institute for Particle Physics & Astrophysics

4. Benjamin M. Taysum
   Affiliation as printed

   Institute for Space Research

5. John Lee Grenfell

   Freie Universität Berlin

   Affiliation as printed

   Free University of Berlin

   Institute for Space Research

6. Tim Lichtenberg

   University of Groningen

   Affiliation as printed

   Kapteyn Astronomical Institute of the University of Groningen

7. Daniel Kitzmann

   University of Bern

   Affiliation as printed

   University of Bern

8. Floris F. S. van der Tak Aachen Space Research Organisation Netherlands

   University of Groningen · Space Research Organisation Netherlands

   Affiliation as printed

   Kapteyn Astronomical Institute of the University of Groningen

   Space Research Organisation Netherlands (SRON)

9. Sascha P. Quanz

   Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Department of Earth and Planetary Sciences

   Institute for Particle Physics & Astrophysics