Atmospheric Constraints On GJ 1214 b From CRIRES+ And Prospects For Characterisation With ANDES

In this study, we aim to constrain the atmospheric composition of GJ 1214 b using all available transits observed with the upgraded CRIRES+ spectrograph at the VLT by searching for the signatures of water vapour, methane, and carbon dioxide.

We analysed eight CRIRES+ transit datasets covering the K band (1.90-2.45 microns) at a resolving power of R ~ 100,000. We used the SysRem algorithm to correct for telluric and stellar contributions and employed the cross-correlation technique with templates from petitRADTRANS to search for H₂O, CH4, and CO₂.

Injection-recovery tests across a grid of metallicities (Z) and cloud-deck pressures (pc) were performed to quantify detection limits. We also generated predictions for ANDES observations using end-to-end simulated datasets with EXoPLORE. We detect no significant H₂O, CH₄, or CO₂ signatures.

Injection-recovery tests show that such non-detections exclude atmospheres with low-altitude clouds and moderate or low metallicities. CH₄ yields the tightest empirical limits, with CO₂ unexpectedly ruling out intermediate metallicities (~ 100xsolar) with clouds deeper due to its rapidly rising opacity in compressed, high-Z atmospheres.

Our constraints are in line with either a high-Z or a high-altitude aerosol layer, in agreement with recent JWST inferences. The combined analysis of eight CRIRES+ datasets provides the most stringent high-resolution constraints on the atmospheric properties of GJ 1214 b to date.

Simulations of a single transit observed with ANDES on the ELT predict modest improvements for H₂O, a substantially expanded detectable region for CH₄, and the strongest gains for CO₂, making the latter a particularly effective tracer for characterising high-metallicity atmospheres in sub-Neptunes.

A. Peláez-Torres, A. Sánchez-López, C. Jiang, E. Pallé, J. Orell-Miquel, M. López-Puertas, L. T. Parker, H. Diamond-Lowe

Comments: 13 pages, 12 figures, accepted for publication in A&A. arXiv admin note: text overlap with arXiv:2512.04161
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2602.14343 [astro-ph.EP] (or arXiv:2602.14343v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2602.14343
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Submission history
From: Alberto Peláez Torres
[v1] Sun, 15 Feb 2026 23:20:04 UTC (32,065 KB)
https://arxiv.org/abs/2602.14343
Astrobiology, exoplanet,