Year: 2026
Type: article
Abstract: The elemental compositions of exoplanets encode information about their formation environments and internal structures. While volatile ratios such as carbon-to-oxygen (C/O) are used to trace formation location, the rock-forming elements–magnesium (Mg), silicon (Si), and iron (Fe)–govern interior mineralogy and are commonly assumed to reflect the host star’s abundances. Yet this assumption remains largely untested. Ultra-hot Jupiters, gas-giant exoplanets with dayside temperatures above 3000 K, provide rare access to refractory elements that remain gaseous. Here we present high-resolution thermal emission spectroscopy of the exoplanet WASP-189b ( $${T}_{eq}=335{4}_{-34}^{+27}$$ T e q = 335 4 − 34 + 27 K) obtained with the Immersion Grating Infrared Spectrometer (IGRINS) on Gemini South. We detect neutral iron (Fe i ), magnesium (Mg i ), silicon (Si i ), water (H 2 O), carbon monoxide (CO), and hydroxyl (OH) at signal-to-noise ratios exceeding 4, and retrieve their elemental abundances. We show that the Mg/Si, Fe/Mg, and Si/Fe ratios are consistent with stellar values, while the refractory-to-volatile ratio is enhanced by roughly a factor of 2. These findings demonstrate that giant-planet atmospheres can preserve stellar-like rock-forming ratios, providing an empirical validation of the stellar-proxy assumption that underpins planetary composition and formation models across exoplanet systems.
Source: Nature Communications
Authors: Jorge A. Sanchez, Peter C. B. Smith, Krishna Kanumalla, Luis Welbanks, Michael R. Line, Stefan Pelletier, Steven Desch, Patrick Young, Jennifer Patience, Jacob Bean, Matteo Brogi, Dan Jaffe, Gregory N. Mace, Megan Weiner Mansfield, Vatsal Panwar, Vivien Parmentier, Lorenzo Pino, Arjun Baliga Savel, Lennart van Sluijs, Joost P. Wardenier
Institutions: Arizona State University, University of Geneva, University of Chicago, Osservatorio Astrofisico di Torino, University of Turin, National Institute for Astrophysics, The University of Texas at Austin, University of Maryland, College Park, University of Warwick, University of Birmingham, Centre National de la Recherche Scientifique, Université Côte d'Azur, Lagrange Laboratory, Observatoire de la Côte d’Azur, Arcetri Astrophysical Observatory, University of Michigan, University of Bern, Université de Montréal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $6,990
Funders: National Science Foundation, National Aeronautics and Space Administration, Arizona State University, University of Texas at Austin, Ministry of Science, ICT and Future Planning, Nuclear Safety and Security Commission, Korea Astronomy and Space Science Institute, Agencia Nacional de Investigación y Desarrollo, Science Mission Directorate
Awards: MRI: Development of a High Resolution Infrared Spectrograph with a Large Spectral Grasp, G3829994955, MAPS: The MMT Adaptive optics exoPlanet characterization System, Enabling a New Instrument 'IGRINS' for the Gemini South Telescope User Community, Collaborative Research: Revealing Exoplanet Atmospheres Using High-Resolution Spectroscopy, G8144931456
OpenAlex ID: W7130428445