Escaping Helium and a Highly Muted Spectrum Suggest a Metal-enriched Atmosphere on Sub-Neptune GJ 3090 b from JWST Transit Spectroscopy

Abstract Sub-Neptunes, the most common planet type, remain poorly understood. Their atmospheres are expected to be diverse, but their compositions are challenging to determine, even with JWST. Here, we present the first JWST spectroscopic study of the warm sub-Neptune GJ 3090 b (2.13 R ⊕ , T eq,A = 0.3 ∼ 700 K), which orbits an M2V star, making it a favorable target for atmosphere characterization. We observed four transits of GJ 3090 b: two each using JWST NIRISS/SOSS and NIRSpec/G395H, yielding wavelength coverage from 0.6 to 5.2 μ m. We detect the signature of the 10833 Å metastable helium triplet at a statistical significance of 5.5 σ with an amplitude of 434 ± 79 ppm, marking the first such detection in a sub-Neptune with JWST. This amplitude is significantly smaller than predicted by solar-metallicity forward models, suggesting a metal-enriched atmosphere that decreases the mass-loss rate and attenuates the helium feature amplitude. Moreover, we find that stellar contamination, in the form of the transit light source effect, dominates the NIRISS transmission spectra, with unocculted spot and faculae properties varying across the two visits separated in time by approximately 6 months. Free retrieval analyses on the NIRSpec/G395H spectrum find tentative evidence for highly muted features and a lack of CH 4 . These findings are best explained by a high-metallicity atmosphere (>100× solar at 3 σ confidence for clouds at ∼ μ bar pressures) using chemically consistent retrievals and self-consistent model grids. Further observations of GJ 3090 b are needed for tighter constraints on the atmospheric abundances and to gain a deeper understanding of the processes that led to its potential metal enrichment.

Authors

Publication Details

Journal
The Astrophysical Journal Letters
Published
2025-05-14
DOI
https://doi.org/10.3847/2041-8213/add010
Citations
17
Primary Topic
Gamma-ray bursts and supernovae
Type
article
Field-Weighted Citation Impact
19.63

Funders

Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
article

Escaping Helium and a Highly Muted Spectrum Suggest a Metal-enriched Atmosphere on Sub-Neptune GJ 3090 b from JWST Transit Spectroscopy

Raymond T. Pierrehumbert, René Doyon, Caroline Piaulet, Eva-Maria Ahrer et al.
17 citations
The Astrophysical Journal Letters
Gamma-ray bursts and supernovae
19.63
article

Escaping Helium and a Highly Muted Spectrum Suggest a Metal-enriched Atmosphere on Sub-Neptune GJ 3090 b from JWST Transit Spectroscopy

Raymond T. Pierrehumbert, René Doyon, Caroline Piaulet, Eva-Maria Ahrer, Duncan Christie, Louis-Philippe Coulombe, Ryan Cloutier, Thaddeus D. Komacek, Charles Cadieux, Luis Welbanks, Jonathan J. Fortney, Heather A. Knutson, Hamish Innes, Joshua Krissansen‐Totton, Romain Allart, Pierre-Alexis Roy, Morgan Saidel, Lindsey S. Wiser, Ryan J. MacDonald, Michael Radica, T. M. Evans, Yamila Miguel, Thomas G. Beatty, Amy Louca, L. Acuña, Björn Benneke, Cyril Gapp, Anna Gagnebin, Eshan Raul, Hilke E. Schlichting
article en
17 citations

Abstract

Abstract Sub-Neptunes, the most common planet type, remain poorly understood. Their atmospheres are expected to be diverse, but their compositions are challenging to determine, even with JWST. Here, we present the first JWST spectroscopic study of the warm sub-Neptune GJ 3090 b (2.13 R ⊕ , T eq,A = 0.3 ∼ 700 K), which orbits an M2V star, making it a favorable target for atmosphere characterization. We observed four transits of GJ 3090 b: two each using JWST NIRISS/SOSS and NIRSpec/G395H, yielding wavelength coverage from 0.6 to 5.2 μ m. We detect the signature of the 10833 Å metastable helium triplet at a statistical significance of 5.5 σ with an amplitude of 434 ± 79 ppm, marking the first such detection in a sub-Neptune with JWST. This amplitude is significantly smaller than predicted by solar-metallicity forward models, suggesting a metal-enriched atmosphere that decreases the mass-loss rate and attenuates the helium feature amplitude. Moreover, we find that stellar contamination, in the form of the transit light source effect, dominates the NIRISS transmission spectra, with unocculted spot and faculae properties varying across the two visits separated in time by approximately 6 months. Free retrieval analyses on the NIRSpec/G395H spectrum find tentative evidence for highly muted features and a lack of CH 4 . These findings are best explained by a high-metallicity atmosphere (>100× solar at 3 σ confidence for clouds at ∼ μ bar pressures) using chemically consistent retrievals and self-consistent model grids. Further observations of GJ 3090 b are needed for tighter constraints on the atmospheric abundances and to gain a deeper understanding of the processes that led to its potential metal enrichment.

The Astrophysical Journal LettersVol. 985(1)
National Science Foundation, National Aeronautics and Space Administration, Space Telescope Science Institute, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Max-Planck-Gesellschaft, Natural Sciences and Engineering Research Council of Canada, Fonds de recherche du Québec – Nature et technologies
Openalex Percentile: Top 1%
Gamma-ray bursts and supernovae
19.63
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.