Evidence for SiO cloud nucleation in the rogue planet PSO J318

Silicate clouds have long been known to significantly impact the spectra of late L-type brown dwarfs – with observable absorption features at ~10 μm. The James Webb Space Telescope (JWST) has reopened a window to the mid-infrared with unprecedented sensitivity, bringing the characterization of silicate clouds into focus again. Using JWST, we aim to characterize the planetary-mass brown dwarf PSO J318.5338-22.8603, concentrating on any silicate cloud absorption the object may exhibit. PSO J318’s spectrum is extremely red, and its flux is variable, both of which are thought to be hallmarks of cloud absorption. We present JWST NIRSpec PRISM, G395H, and MIRI MRS observations of PSO J318 from 1 to 18 μm. We introduce a method based on PSO J318’s brightness temperature to generate a list of cloud species that are likely present in its atmosphere. We tested for the species’ presence with petitRADTRANS retrievals. Using retrievals and grids from various climate models, we derived bulk parameters from PSO J318’s spectra, which are mutually compatible. Our retrieval results point to a solar to a slightly super-solar atmospheric C/O, a slightly super-solar metallicity, and a 12 C/ 13 C below ISM values. The atmospheric gravity proves difficult to constrain for both retrievals and grid models. Retrievals describing the flux of PSO J318 by mixing two 1D models (“two-column models”) appear favored over single-column models; this is consistent with PSO J318’s variability. The JWST observations also reveal a pronounced absorption feature at 10 μm. This absorption is best reproduced by introducing a high-altitude cloud layer of small (<0.1 μm) amorphous SiO grains. The retrieved particle size and location of the cloud is consistent with SiO condensing as cloud seeding nuclei. High-altitude clouds comprised of small SiO particles have been suggested in previous studies. Therefore, the SiO nucleation we potentially observe in PSO J318 could be a more widespread phenomenon.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2025-09-30
DOI
https://doi.org/10.1051/0004-6361/202555732
Citations
5
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
5.77
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article

Evidence for SiO cloud nucleation in the rogue planet PSO J318

Alistair Glasse, M. Guêdel, G. Olofsson, C. Jäger et al.
5 citations
Astronomy and Astrophysics
Stellar, planetary, and galactic studies
5.77
article

Evidence for SiO cloud nucleation in the rogue planet PSO J318

Alistair Glasse, M. Guêdel, G. Olofsson, C. Jäger, Ioannis Argyriou, Pascal Tremblin, Niall Whiteford, Zhi-Yu Zhang, M. Min, Göran Östlin, Beth Biller, L. Decin, T. P. Ray, Christophe Cossou, Silvia Scheithauer, Olivier Absil, D. Barrado, J. P. Pye, Polychronis Patapis, M. Samland, P. Mollière, Daniel Rouan, Elisabeth C. Matthews, Th. Henning, L. B. F. M. Waters, Pierre-Olivier Lagage, E. F. van Dishoeck, H. Kühnle
article en
5 citations

Abstract

Silicate clouds have long been known to significantly impact the spectra of late L-type brown dwarfs – with observable absorption features at ~10 μm. The James Webb Space Telescope (JWST) has reopened a window to the mid-infrared with unprecedented sensitivity, bringing the characterization of silicate clouds into focus again. Using JWST, we aim to characterize the planetary-mass brown dwarf PSO J318.5338-22.8603, concentrating on any silicate cloud absorption the object may exhibit. PSO J318’s spectrum is extremely red, and its flux is variable, both of which are thought to be hallmarks of cloud absorption. We present JWST NIRSpec PRISM, G395H, and MIRI MRS observations of PSO J318 from 1 to 18 μm. We introduce a method based on PSO J318’s brightness temperature to generate a list of cloud species that are likely present in its atmosphere. We tested for the species’ presence with petitRADTRANS retrievals. Using retrievals and grids from various climate models, we derived bulk parameters from PSO J318’s spectra, which are mutually compatible. Our retrieval results point to a solar to a slightly super-solar atmospheric C/O, a slightly super-solar metallicity, and a 12 C/ 13 C below ISM values. The atmospheric gravity proves difficult to constrain for both retrievals and grid models. Retrievals describing the flux of PSO J318 by mixing two 1D models (“two-column models”) appear favored over single-column models; this is consistent with PSO J318’s variability. The JWST observations also reveal a pronounced absorption feature at 10 μm. This absorption is best reproduced by introducing a high-altitude cloud layer of small (<0.1 μm) amorphous SiO grains. The retrieved particle size and location of the cloud is consistent with SiO condensing as cloud seeding nuclei. High-altitude clouds comprised of small SiO particles have been suggested in previous studies. Therefore, the SiO nucleation we potentially observe in PSO J318 could be a more widespread phenomenon.

Astronomy and AstrophysicsVol. 703
Leiden University (NL), Centre National de la Recherche Scientifique (FR), University of Vienna (AT), Dublin Institute For Advanced Studies (IE), American Museum of Natural History (US), Radboud University Nijmegen (NL), University of Leicester (GB), University of Liège (BE), Schiller International University (FR), Université de Versailles Saint-Quentin-en-Yvelines (FR), Université Paris Cité (FR), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris-Saclay (FR), NASA Exoplanet Science Institute (US), ETH Zurich (CH), Sorbonne Université (FR), Astrophysique, Instrumentation et Modélisation (FR), Sorbonne Paris Cité (FR), Institute of Particle Physics (CA), Royal Observatory (GB), Max Planck Institute for Astronomy (DE), Institute of Astronomy (RU), Maison de la Simulation (FR), CEA Paris-Saclay (FR), Centro de Astrobiología (ES), AlbaNova (SE), Astronomy and Space (AU), Institut de Recherche sur les Lois Fondamentales de l'Univers (FR), Space Research Organisation Netherlands (NL), UK Astronomy Technology Centre (GB), University of Rochester (US), Inter-University Centre for Astronomy and Astrophysics (IN), Netherlands Institute for Radio Astronomy (NL), University of Edinburgh (GB), KU Leuven (BE)
Openalex Percentile: Top 4%
Stellar, planetary, and galactic studies
5.77
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