Cloudy with a chance of metals: Indications of CO$_2$ in the atmosphere of GJ 1214 b from high-resolution K-band spectroscopy
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| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866911599211577344 |
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| author | Nortmann, L. Cont, D. Lesjak, F. Rains, A. D. Lavail, A. Boldt-Christmas, L. Nagel, E. Reiners, A. Piskunov, N. Yan, F. Hatzes, A. Kochukhov, O. Shulyak, D. Seemann, U. Rengel, M. Hahlin, A. |
| author_facet | Nortmann, L. Cont, D. Lesjak, F. Rains, A. D. Lavail, A. Boldt-Christmas, L. Nagel, E. Reiners, A. Piskunov, N. Yan, F. Hatzes, A. Kochukhov, O. Shulyak, D. Seemann, U. Rengel, M. Hahlin, A. |
| contents | Sub-Neptune exoplanets frequently exhibit muted transmission spectra, with GJ 1214 b being the most prominent example. Following years of intense observing campaigns yielding featureless planetary spectra, recent observations with JWST revealed the first possible atmospheric signatures. We present high-resolution transmission spectroscopy of GJ 1214 b based on eight transits obtained with the CRIRES$^+$ spectrograph in the K band. We used SYSREM to remove telluric and stellar signals and searched for signatures of H2O, CO, CH4, H2S, NH3, and CO2 using the cross-correlation technique. We obtained non-detections for the first five molecules and used injection recovery tests to derive upper limits on the atmosphere. For CO$_2$ we measure a CCF signal at S/N ~ 3.6, with a detailed investigation showing no obvious indication that it is caused by correlated noise. A Welch t-test confirmed the in-trail and out-of-trail distributions to be different at $3.4 σ$ confidence. A Bayesian retrieval framework with free chemistry, resulted in volume mixing ratios corresponding to a metallicity of $[\mathrm{M/H}]=0.48^{+0.89}_{-1.70}$, an opacity deck pressure of $\log_{10}(P_\mathrm{c}) = -3.04^{+2.52}_{-1.53}$ and a planet temperature of $T_\mathrm{iso}=398^{+283}_{-197}$ K, consistent with a value intermediate between the day- and night-side T-p's derived from JWST data. While these values correspond to relatively large signal amplitudes predicted for CO2 features in the mid-infrared, they are compatible with JWST NIRSpec observations within the models' $1.5σ$ uncertainties. Further modelling and additional data are required to confirm the atmospheric signatures and obtain a comprehensive interpretation of low- and high-resolution data. Overall, our results support previous findings that CO2 is likely to be a significant component of the atmosphere of GJ 1214 b. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_15292 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Cloudy with a chance of metals: Indications of CO$_2$ in the atmosphere of GJ 1214 b from high-resolution K-band spectroscopy Nortmann, L. Cont, D. Lesjak, F. Rains, A. D. Lavail, A. Boldt-Christmas, L. Nagel, E. Reiners, A. Piskunov, N. Yan, F. Hatzes, A. Kochukhov, O. Shulyak, D. Seemann, U. Rengel, M. Hahlin, A. Earth and Planetary Astrophysics Sub-Neptune exoplanets frequently exhibit muted transmission spectra, with GJ 1214 b being the most prominent example. Following years of intense observing campaigns yielding featureless planetary spectra, recent observations with JWST revealed the first possible atmospheric signatures. We present high-resolution transmission spectroscopy of GJ 1214 b based on eight transits obtained with the CRIRES$^+$ spectrograph in the K band. We used SYSREM to remove telluric and stellar signals and searched for signatures of H2O, CO, CH4, H2S, NH3, and CO2 using the cross-correlation technique. We obtained non-detections for the first five molecules and used injection recovery tests to derive upper limits on the atmosphere. For CO$_2$ we measure a CCF signal at S/N ~ 3.6, with a detailed investigation showing no obvious indication that it is caused by correlated noise. A Welch t-test confirmed the in-trail and out-of-trail distributions to be different at $3.4 σ$ confidence. A Bayesian retrieval framework with free chemistry, resulted in volume mixing ratios corresponding to a metallicity of $[\mathrm{M/H}]=0.48^{+0.89}_{-1.70}$, an opacity deck pressure of $\log_{10}(P_\mathrm{c}) = -3.04^{+2.52}_{-1.53}$ and a planet temperature of $T_\mathrm{iso}=398^{+283}_{-197}$ K, consistent with a value intermediate between the day- and night-side T-p's derived from JWST data. While these values correspond to relatively large signal amplitudes predicted for CO2 features in the mid-infrared, they are compatible with JWST NIRSpec observations within the models' $1.5σ$ uncertainties. Further modelling and additional data are required to confirm the atmospheric signatures and obtain a comprehensive interpretation of low- and high-resolution data. Overall, our results support previous findings that CO2 is likely to be a significant component of the atmosphere of GJ 1214 b. |
| title | Cloudy with a chance of metals: Indications of CO$_2$ in the atmosphere of GJ 1214 b from high-resolution K-band spectroscopy |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2604.15292 |