Silicate Precursor Silane detected in Cold Low-Metallicity Brown Dwarf
Abstract
Within 20 pc of the Sun there are currently 29 known cold brown dwarfs, sources with measured distances and an estimated effective temperature between that of Jupiter (170K) and ~500K. These sources are almost all isolated and are the closest laboratories we have for detailed atmospheric studies of giant planets formed outside the solar system. Here we report JWST observations of one such source, WISEA J153429.75-104303.3 (W1534), which we confirm is a substellar mass member of the Galactic halo with a metallicity <0.01xsolar. Its spectrum reveals methane (CH4), water (H2O), and silane (SiH4) gas. Although SiH4 is expected to serve as a key reservoir for the cloud-forming element Si in gas giant worlds, it eluded detection until now because it is removed from observable atmospheres by the formation of silicate clouds at depth. These condensates are favored with increasing metallicity, explaining why SiH4 remains undetected on well studied, metal-rich solar system worlds like Jupiter and Saturn. On the metal-poor world W1534, we detect a clear signature of SiH4 centered at ~4.55 microns with an abundance of 19+/-2 parts per billion (ppb). Our chemical modelling suggests that this SiH4 abundance may be quenched at ~kilobar levels just above the silicate cloud layers, whereupon vertical atmospheric mixing can transport SiH4 to the observable photosphere. The formation and detection of SiH4 demonstrates key coupled relationships between composition, cloud formation, and atmospheric mixing in cold brown dwarf and planetary atmospheres.
Cite
@article{arxiv.2509.18635,
title = {Silicate Precursor Silane detected in Cold Low-Metallicity Brown Dwarf},
author = {Jacqueline K. Faherty and Aaron M. Meisner and Ben Burningham and Channon Visscher and Michael Line and Genaro Suarez and Jonathan Gagne and Sherelyn Alejandro Merchan and Austin James Rothermich and Adam J. Burgasser and Adam C. Schneider and Dan Caselden and J. Davy Kirkpatrick and Marc Jason Kuchner and Daniella Carolina Bardalez Gagliuffi and Peter Eisenhardt and Christopher R. Gelino and Eileen C. Gonzales and Federico Marocco and Sandy Leggett and Nicolas Lodieu and Sarah L. Casewell and Pascal Tremblin and Michael Cushing and Maria Rosa Zapatero Osorio and Victor J. S. Bejar and Bartosz Gauza and Edward Wright and Mark W. Phillips and Jun-Yan Zhang and Eduardo L. Martin},
journal= {arXiv preprint arXiv:2509.18635},
year = {2025}
}
Comments
Accepted by Nature. 31 pages, 9 figures, 3 tables https://doi.org/10.1038/s41586-025-09369-1