Large Interferometer For Exoplanets (LIFE)

I. Improved exoplanet detection yield estimates for a large mid-infrared space-interferometer mission

¹ ETH Zurich, Institute for Particle Physics & Astrophysics, Wolfgang-Pauli-Str. 27, 8093 Zurich, Switzerland
e-mail: sascha.quanz@phys.ethz.ch
² National Center of Competence in Research PlanetS, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁴ Research School of Astronomy & Astrophysics, Australian National University, ACT 2611, Australia
⁵ STAR Institute, University of Liège, 19C allée du Six Aout, 4000 Liège, Belgium
⁶ NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD, 20771 USA
⁷ Department of Physics, and Institute for Research on Exoplanets, Université de Montréal, Montréal H3T 1J4, Canada
⁸ University of Oxford, Department of Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, Sherrington Road, Oxford OX1 3PU, UK
⁹ DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 328, DK-2800 Kgs. Lyngby, Denmark
¹⁰ Department of Extrasolar Planets and Atmospheres, Institute for Planetary Research, German Aerospace Centre, Rutherfordstr. 2, 12489 Berlin, Germany
¹¹ Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany
¹² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹³ Centre Spatial de Liège, Université de Liège, Avenue Pré-Aily, 4031 Angleur, Belgium
¹⁴ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
¹⁵ University of Zurich, Institute of Computational Sciences, Winterthurerstrasse 190, 8057 Zurich, Switzerland
¹⁶ Observatoire astronomique de l’Université de Genève, chemin Pegasi 51b, 1290 Versoix, Switzerland
¹⁷ Large Binocular Telescope Observatory, 933 North Cherry Avenue, Tucson, AZ 85721 USA
¹⁸ Steward Observatory, Department of Astronomy, University of Arizona, 993 N. Cherry Ave, Tucson, AZ, 85721 USA
¹⁹ Leiden Observatory, Leiden University, 2333CA Leiden, The Netherlands
²⁰ Department of Space, Earth & Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
²¹ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, C/Can Magrans s/n, 08193 Bellaterra, Spain
²² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 USA
²³ Department of Astronomy, Stockholm University, Alba Nova University Center, 10691 Stockholm, Sweden
²⁴ Department of Space, Earth and Environment, Astronomy and Plasma Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
²⁵ University of Exeter, School of Physics and Astronomy, Stocker Road, Exeter EX4 4QL, UK
²⁶ IAS, CNRS (UMR 8617), bât 121, Univ. Paris-Sud, 91405 Orsay, France
²⁷ University of Tartu, Tartu Observatory, 1 Observatooriumi Str., 61602 Tõravere, Tartumaa, Estonia
²⁸ Centro de Astrobiología (CAB, CSIC-INTA), Depto. de Astrofísica, ESAC campus 28692 Villanueva de la Cañada (Madrid), Spain
²⁹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³⁰ SRM Institute of Science and Technology, Chennai, India
³¹ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 USA
³² Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 USA
³³ Physikalisches Institut, Universität Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
³⁴ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
³⁵ Freie Universitat Berlin, Department of Earth Sciences, Malteserstr. 74–100, 12249 Berlin, Germany
³⁶ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
³⁷ Dept. Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³⁸ Institut d’Estudis Espacials de Catalunya (IEEC), C/Gran Capitá 2–4, 08034 Barcelona, Spain
³⁹ Department of Astronomy, Yale University, New Haven, CT 06511 USA
⁴⁰ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00–716 Warsaw, Poland
⁴¹ Department of Earth and Planetary Sciences, University of California, Riverside, 900 University Ave. Riverside, CA 92521 USA
⁴² Deshbandhu College, University of Delhi 110019 Delhi, India
⁴³ Vanderbilt University, Department of Physics & Astronomy, 6301 Stevenson Center Ln., Nashville, TN 37235 USA
⁴⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴⁵ Large Interferometer For Exoplanets, Exoplanets and Habitability Group, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland

Received: 16 January 2021
Accepted: 31 March 2022

Abstract

Context. One of the long-term goals of exoplanet science is the atmospheric characterization of dozens of small exoplanets in order to understand their diversity and search for habitable worlds and potential biosignatures. Achieving this goal requires a space mission of sufficient scale that can spatially separate the signals from exoplanets and their host stars and thus directly scrutinize the exoplanets and their atmospheres.

Aims. We seek to quantify the exoplanet detection performance of a space-based mid-infrared (MIR) nulling interferometer that measures the thermal emission of exoplanets. We study the impact of various parameters and compare the performance with that of large single-aperture mission concepts that detect exoplanets in reflected light.

Methods. We have developed an instrument simulator that considers all major astrophysical noise sources and coupled it with Monte Carlo simulations of a synthetic exoplanet population around main-sequence stars within 20 pc of the Sun. This allows us to quantify the number (and types) of exoplanets that our mission concept could detect. Considering single visits only, we discuss two different scenarios for distributing 2.5 yr of an initial search phase among the stellar targets. Different apertures sizes and wavelength ranges are investigated.

Results. An interferometer consisting of four 2 m apertures working in the 4–18.5 μ.m wavelength range with a total instrument throughput of 5% could detect up to ≈550 exoplanets with radii between 0.5 and 6 R_⊕ with an integrated S/N ≥ 7. At least ≈160 of the detected exoplanets have radii ≤1.5 R_⊕. Depending on the observing scenario, ≈25–45 rocky exoplanets (objects with radii between 0.5 and 1.5 R_⊕) orbiting within the empirical habitable zone (eHZ) of their host stars are among the detections. With four 3.5 m apertures, the total number of detections can increase to up to ≈770, including ≈60–80 rocky eHZ planets. With four times 1 m apertures, the maximum detection yield is ≈315 exoplanets, including ≤20 rocky eHZ planets. The vast majority of small, temperate exoplanets are detected around M dwarfs. The impact of changing the wavelength range to 3–20 μm or 6–17 μm on the detection yield is negligible.

Conclusions. A large space-based MIR nulling interferometer will be able to directly detect hundreds of small, nearby exoplanets, tens of which would be habitable world candidates. This shows that such a mission can compete with large single-aperture reflected light missions. Further increasing the number of habitable world candidates, in particular around solar-type stars, appears possible via the implementation of a multi-visit strategy during the search phase. The high median S/N of most of the detected planets will allow for first estimates of their radii and effective temperatures and will help prioritize the targets for a second mission phase to obtain high-S/N thermal emission spectra, leveraging the superior diagnostic power of the MIR regime compared to shorter wavelengths.