Constraining small planet compositions for future missions
Year: 2026
Type: article
Abstract: ABSTRACT Accurate mass and radius measurements of small transiting exoplanets are essential for probing their compositions, formation histories, and potential habitability. We present a uniform analysis of six planetary systems (each hosting at least one small transiting planet): K2-79, K2-106, K2-111, K2-222, K2-263, and TOI-1634. Our study combines new CHEOPS transit observations with archival photometry from K2, TESS, and ground-based facilities, alongside new and archival radial velocity data from HARPS-N, HIRES, ESPRESSO, and others. For each system, we perform joint transit and RV modelling, achieving typical precisions better than 15 per cent and 5 per cent for mass and radius, respectively, and thus enabling precise bulk density determinations. These reveal a range of compositions, including rocky planets near the radius valley (e.g. K2-106 b, TOI-1634 b), intermediate-density planets requiring steam-rich or mixed volatile envelopes (e.g. K2-111 b, K2-263 b), and low-density regimes, consistent with gas dwarfs or water-worlds (e.g. K2-79 b, K2-222 b). Several systems show evidence of additional companions detectable via RVs but not seen in transit. The results highlight the value of coordinated CHEOPS and HARPS-N observations in delivering some of the most precise bulk densities for small planets to date and support the preparation for future atmospheric characterization missions.
Authors: Larissa Palethorpe, Annelies Mortier, Jo Ann Egger, Ken Rice, Thomas G Wilson, Andrew Vanderburg, Aldo S Bonomo, Walter Boschin, Andrew Collier Cameron, Yoshi Nike Emilia Eschen, Avet Harutyunyan, Luca Malavolta, Aldo F Martínez Fiorenzano, Alessandro Sozzetti, Manu Stalport, Vincent Van Eylen, Christopher Allan Watson
Institutions: University of Bristol, Royal Observatory, University of Edinburgh, University of Birmingham, University of Bern, European Space Agency, European Space Research and Technology Centre, University of Warwick, Center for Astrophysics Harvard & Smithsonian, Osservatorio Astrofisico di Torino, National Institute for Astrophysics, Telescopio Nazionale Galileo, University of St Andrews, University of Padua, Osservatorio Astronomico di Padova, University of Liège, University College London, Queen's University Belfast
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Funders: National Science Foundation, Smithsonian Institution, National Aeronautics and Space Administration, California Institute of Technology, Harvard University, UK Space Agency, Space Telescope Science Institute, UK Research and Innovation, European Space Agency, Royal Society, Scottish Universities Physics Alliance, University of St Andrews, University of Warwick, Queen's University Belfast, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Belgian Federal Science Policy Office, Queen's University, Mitutoyo Association for Science and Technology, Université de Genève, Institut sur la Nutrition et les Aliments Fonctionnels, Smithsonian Astrophysical Observatory, Science and Technology Facilities Council, Division of Chemistry, H2020 European Research Council
Awards: Astronomy at St Andrews 2021 - 2024, G1508728180, G1646535634, MSSL Astrophysics Consolidated Grant 2022-25, G3170351587, G3174702021, G3330823230, G3881939388, G3992242914, Phasenübergänge und Instabilitäten, G4276578120, G441095050, Queen's University Belfast Astronomy Observation and Theory Consolidated Grant 2023-2026, From oscillations to rotation: Detecting exoplanets through BiSON, Astrophysics Consolidated Grant 2019-22, THE MULTI-MISSION ARCHIVE AT SPACE TELESCOPE SCIENCE INSTITUTE (MAST) IS NASA'S ARCHIVE CENTER FOR OPTICAL/UV SPACE ASTROPHYSICS DATA. MAST PROVIDE, G58316358, G5964941315, G6273510985, G6295302557, NCCR PlanetS: Origin, evolution and characterisation of planets, G7101938745, G8081747916, G8318038168, G8377147572, G8505061131, STFC Warwick 2023 DTP
OpenAlex ID: W7140167934