Escaping Helium and a Highly Muted Spectrum Suggest a Metal-Enriched Atmosphere on Sub-Neptune GJ3090b 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 GJ3090b (2.13R${}_{\oplus }$, Teq~700 K) which orbits an M2V star, making it a favourable target for atmosphere characterization. We observed four transits of GJ3090b; two each using JWST NIRISS/SOSS and NIRSpec/G395H, yielding wavelength coverage from 0.6-5.2 $\mu$m. We detect the signature of the 10833 Å metastable Helium triplet at a statistical significance of 5.5$\sigma$ with an amplitude of 434$\pm$79 ppm, marking the first such detection in a sub-Neptune with JWST. This amplitude is significantly smaller than predicted by solar-metallicity forward models, suggesting a metal-enriched atmosphere which decreases the mass-loss rate and attenuates the Helium feature amplitude. Moreover, we find that stellar contamination, in the form of the transit light source effect, dominates the NIRISS transmission spectra, with unocculted spot and faculae properties varying across the two visits separated in time by approximately six months. Free retrieval analyses on the NIRSpec/G395H spectrum find tentative evidence for highly muted features and a lack of CH4. These findings are best explained by a high metallicity atmosphere (>100x solar at 3$\sigma$ confidence, for clouds at $\sim \mu$bar pressures) using chemically-consistent retrievals and self-consistent model grids. Further observations of GJ3090b 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.

36 pages, 21 figures, accepted for publication in ApJL

References in corpus (92)

• Array Programming with NumPy
• The Transiting Exoplanet Survey Satellite
• Bayes in the sky: Bayesian inference and model selection in cosmology
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• PolyChord: nested sampling for cosmology
• Roche lobe effects on the atmospheric loss of "Hot Jupiters"
• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars
• Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H
• Photochemically-produced SO${}_2$ in the atmosphere of WASP-39b
• ExoMol molecular line lists XXXV: a rotation-vibration line list for hot ammonia
• A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
• ExoMol molecular line lists - XVI: The rotation-vibration spectrum of hot H${}_2$S
• Early Release Science of the exoplanet WASP-39b with JWST NIRISS
• ExoMol line lists -- XXXIX. Ro-vibrational molecular line list for CO${}_2$
• No thick carbon dioxide atmosphere on the rocky exoplanet TRAPPIST-1 c
• Early Release Science of the exoplanet WASP-39b with JWST NIRCam
• High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations
• Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra
• A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curve
• Habitable Evaporated Cores: Transforming Mini-Neptunes into Super-Earths in the Habitable Zones of M Dwarfs
• Habitability and Biosignatures of Hycean Worlds
• Eureka!: An End-to-End Pipeline for JWST Time-Series Observations
• The Transit Light Source Effect II: The Impact of Stellar Heterogeneity on Transmission Spectra of Planets Orbiting Broadly Sun-like Stars
• A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b
• High-resolution confirmation of an extended helium atmosphere around WASP-107b
• The California-Kepler Survey. X. The Radius Gap as a Function of Stellar Mass, Metallicity, and Age
• Beyond Equilibrium Temperature: How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets
• Mass-radius relationships for irradiated ocean planets
• Where is the Water? Jupiter-like C/H ratio but strong H${}_2$O depletion found on $\tau$ Boötis b using SPIRou
• Photoevaporation vs. core-powered mass-loss: model comparison with the 3D radius gap
• A High Internal Heat Flux and Large Core in a Warm Neptune Exoplanet
• Spectroscopic line parameters of NO, NO${}_2$, and N${}_2$O for the HITEMP database
• Conclusive evidence for a population of water-worlds around M-dwarfs remains elusive
• Double Trouble: Two Transits of the Super-Earth GJ 1132 b Observed with JWST NIRSpec G395H
• On degeneracies in retrievals of exoplanetary transmission spectra
• Superabundance of Exoplanet Sub-Neptunes Explained by Fugacity Crisis
• Water on Hot Rocky Exoplanets
• Formation and composition of planets around very low mass stars
• JWST/NIRISS reveals the water-rich "steam world" atmosphere of GJ 9827 d
• Confirmation of WASP-107b's extended Helium atmosphere with Keck II/NIRSPEC
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope IV. Capabilities and predicted performance for exoplanet characterization
• The SPHINX M-dwarf Spectral Grid. I. Benchmarking New Model Atmospheres to Derive Fundamental M-Dwarf Properties
• POSEIDON: A Multidimensional Atmospheric Retrieval Code for Exoplanet Spectra
• Awesome SOSS: Transmission Spectroscopy of WASP-96b with NIRISS/SOSS
• A unique hot Jupiter spectral sequence with evidence for compositional diversity
• The Hazy and Metal-Rich Atmosphere of GJ 1214 b Constrained by Near and Mid-Infrared Transmission Spectroscopy
• Distinguishing oceans of water from magma on mini-Neptune K2-18b
• ACCESS & LRG-BEASTS: a precise new optical transmission spectrum of the ultrahot Jupiter WASP-103b
• Detection of Atmospheric Escape from Four Young Mini Neptunes
• p-winds: an open-source Python code to model planetary outflows and upper atmospheres
• TRIDENT: A Rapid 3D Radiative Transfer Model for Exoplanet Transmission Spectra
• Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b
• Aurora: A Generalised Retrieval Framework for Exoplanetary Transmission Spectra
• Majority of water hides deep in the interiors of exoplanets
• Detection of Ongoing Mass Loss from HD 63433c, a Young Mini Neptune
• Near-Infrared Transmission Spectroscopy of HAT-P-18b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST
• Characterisation of the hydrospheres of TRAPPIST-1 planets
• JWST transmission spectroscopy of HD 209458b: a super-solar metallicity, a very low C/O, and no evidence of CH4, HCN, or C2H2
• A fading radius valley towards M-dwarfs, a persistent density valley across stellar types
• Observability of signatures of transport-induced chemistry in clear atmospheres of hot gas giant exoplanets
• Evidence for the volatile-rich composition of a 1.5-$R_{\oplus }$ planet
• The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- III. Single Object Slitless Spectroscopy
• Stellar surface inhomogeneities as a potential source of the atmospheric signal detected in the K2-18 b transmission spectrum
• The post-transit tail of WASP-107b observed at 10830A
• Dry or water world? How the water contents of inner sub-Neptunes constrain giant planet formation and the location of the water ice line
• Irradiation-driven escape of primordial planetary atmospheres I. The ATES photoionization hydrodynamics code
• Hubble Space Telescope transmission spectroscopy for the temperate sub-Neptune TOI-270d: a possible hydrogen-rich atmosphere containing water vapour
• ExoTiC-LD: thirty seconds to stellar limb-darkening coefficients
• Jupiter's formation in the vicinity of the amorphous ice snowline
• The Influence of Stellar Contamination on the Interpretation of Near Infrared Transmission Spectra of Sub-Neptune Worlds around M-Dwarfs
• Hints of a sulfur-rich atmosphere around the 1.6 R${}_{\oplus }$ Super-Earth L98-59 d from JWST NIRSpec G395H transmission spectroscopy
• Rocklines as Cradles for Refractory Solids in the Protosolar Nebula
• Atmospheric retrievals suggest the presence of a secondary atmosphere and possible sulfur species on L 98-59 d from JWST NIRSpec G395H transmission spectroscopy
• APPLESOSS: A Producer of ProfiLEs for SOSS. Application to the NIRISS SOSS Mode
• A 3D picture of moist-convection inhibition in hydrogen-rich atmospheres: Implications for K2-18 b
• Super-Earths and Earth-like Exoplanets
• ATOCA: an algorithm to treat order contamination. Application to the NIRISS SOSS mode
• Mind the gap: Distinguishing disc substructures and their impact on the inner disc composition
• Shallower radius valley around low-mass hosts: Evidence for icy planets, collisions or high-energy radiation scatter
• The MOPYS project: A survey of 70 planets in search of extended He I and H atmospheres. No evidence of enhanced evaporation in young planets
• Water absorption in the transmission spectrum of the water-world candidate GJ9827d
• LRG-BEASTS: sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2
• Helium Enhanced Planets Along the Upper Edge of the Radius Valley
• On the origin of the non-detection of metastable HeI in the upper atmosphere of the hot Jupiter WASP-80b
• GASTLI: An open-source coupled interior-atmosphere model to unveil gas giant composition
• MSG: A software package for interpolating stellar spectra in pre-calculated grids
• A Mini-Chemical Scheme with Net Reactions for 3D GCMs I.: Thermochemical Kinetics
• GJ 3090 b: one of the most favourable mini-Neptune for atmospheric characterisation
• Interior-atmosphere modelling to assess the observability of rocky planets with JWST
• Observing atmospheric escape in sub-Jovian worlds with JWST
• Spelunker: A quick-look Python pipeline for JWST NIRISS FGS Guide Star Data

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• A Validated Low-to-Intermediate Mass Planetary Interior Structure Model and New Mass-Radius Relations
• Sub-Neptunes as Soot Factories: Deep Atmosphere Hydrocarbon Formation and Quenching as the Origin of Sub-Neptune Aerosol Trends
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• Densities of small planets around the M dwarfs TOI-4336 A and TOI-4342 with ESPRESSO: Three sub-Neptunes, one super-Earth, and a Neptune-mass candidate
• KRONOS I: The $1-2.8\mu$m JWST Transmission Spectrum of the 23 Myr V1298 Tau c
• A Search for helium in the atmospheres of three sub-Neptunes and a super-Earth around M-dwarfs
• Using observations of escaping H/He to constrain the atmospheric composition of sub-Neptunes
• NIRPS tightens the mass estimate of GJ 3090 b and detects a planet near the stellar rotation period
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