Large Interferometer for Exoplanets: VIII. Where Is the Phosphine? Observing Exoplanetary PH 3 with a Space-Based Mid-Infrared Nulling Interferometer

Astrobiology, vol. 23, pp. 183–194

Abstract

Phosphine could be a key molecule in the understanding of exotic chemistry that occurs in (exo)planetary atmospheres. While phosphine has been detected in the Solar System's giant planets, it has not been observed in exoplanets to date. In the exoplanetary context, however, it has been theorized to be a potential biosignature molecule. The goal of our study was to identify which illustrative science cases for PH 3 chemistry are observable with a space-based mid-infrared nulling interferometric observatory like the Large Interferometer for Exoplanets (LIFE) concept. We identified a representative set of scenarios for PH 3 detections in exoplanetary atmospheres that vary over the whole dynamic range of the LIFE mission. We used chemical kinetics and radiative transfer calculations to produce forward models of these informative, prototypical observational cases for LIFEsim, our observation simulator software for LIFE. In a detailed, yet first order approximation, it takes a mission like LIFE: (i) about 1 h to find phosphine in a warm giant around a G star at 10 pc, (ii) about 10 h in H 2 or CO 2 dominated temperate super-Earths around M star hosts at 5 pc, (iii) and even in 100 h it seems very unlikely that phosphine would be detectable in a Venus-Twin with extreme PH 3 concentrations at 5 pc. Phosphine in concentrations previously discussed in the literature is detectable in 2 out of the 3 cases, and it is detected about an order of magnitude faster than in comparable cases with James Webb Space Telescope. We show that there is a significant number of objects accessible for these classes of observations. These results will be used to prioritize the parameter range for the next steps with more detailed retrieval simulations. They will also inform timely questions in the early design phase of a mission like LIFE and guide the community by providing easy-to-scale first estimates for a large part of detection space of such a mission.

Authors 11

1. Daniel Angerhausen corresponding

   ETH Zurich · Blue Marble Space Institute of Science · Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Blue Marble Space Institute of Science, Seattle, Washington, USA

   Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

   National Center of Competence in Research PlanetS, Bern, Switzerland

2. Maurice Ottiger

   ETH Zurich · Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

3. Felix Dannert

   ETH Zurich · Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

4. Yamila Miguel Aachen Leiden Observatory SRON Netherlands Institute for Space Research

   Leiden University · Leiden Observatory · Space Research Organisation Netherlands

   Affiliation as printed

   Leiden Observatory, University of Leiden, Leiden, The Netherlands

   SRON Netherlands Institute for Space Research, Utrecht, The Netherlands

5. Clara Sousa‐Silva

   Smithsonian Astrophysical Observatory · Bard College · Center for Astrophysics Harvard & Smithsonian

   Affiliation as printed

   Center for Astrophysics, Harvard-Smithsonian, Cambridge, Massachusetts, USA

   Division of Science, Mathematics, and Computing, Bard College, Annandale-on-Hudson, New York, USA

6. Jens Kammerer

   Space Telescope Science Institute

   Affiliation as printed

   Space Telescope Science Institute, Baltimore, Maryland, USA

7. Franziska Menti

   ETH Zurich · Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

8. Eleonora Alei

   ETH Zurich · Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

   National Center of Competence in Research PlanetS, Bern, Switzerland

9. Björn S. Konrad

   ETH Zurich · Institute for Particle Physics and Astrophysics

   Affiliation as printed

   Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

   National Center of Competence in Research PlanetS, Bern, Switzerland

10. Haiyang S. Wang

    ETH Zurich · Institute for Particle Physics and Astrophysics

    Affiliation as printed

    Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

    National Center of Competence in Research PlanetS, Bern, Switzerland

11. Sascha P. Quanz

    ETH Zurich · Institute for Particle Physics and Astrophysics

    Affiliation as printed

    Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

    National Center of Competence in Research PlanetS, Bern, Switzerland