Exploring the atmosphere of GJ 1132 b with CRIRES+

¹ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
² Deptartamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³ Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
⁴ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁵ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio, Padova, Italy
⁶ California Institute of Technology, NASA Jet Propulsion Laboratory, 4800 Oak Grove Dr, La Cañada Flintridge, CA 91011, USA
⁷ Centro de Astrobiología, CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain

^★ Corresponding authors: epalle@iac.es; yanfei@ustc.edu.cn

Received: 26 November 2024
Accepted: 27 February 2025

Abstract

With a mass, radius, and mean density similar to Earth’s, the rocky planet GJ 1132 b is the first truly small planet for which an atmosphere detection was proposed. If confirmed, ultra-reduced magma outgassing is the only mechanism capable of producing HCN and H₂O in large enough quantities to match the Hubble Space Telescope observations. The proposed atmosphere detection, however, was challenged by reanalysis of the same HST data by different teams. Recent James Webb Space Telescope observations returned ambiguous results due to the unaccounted for variability seen between two different visits. Here we report the analysis of three CRIRES+ transit observations of GJ 1132 b in order to determine the presence or absence of He I, HCN, CH₄, and H₂O in its atmosphere. We are unable to detect the presence of any of these species in the atmosphere of GJ 1132 b assuming a clear, H₂-dominated atmosphere, although we can place upper limits for the volume mixing ratios of CH₄, HCN, and H₂O using injection tests and atmospheric retrievals. These retrieved upper limits show the capability of CRIRES+ at detecting chemical species in rocky exoplanets, if the atmosphere is H₂ dominated. The detection of the atmospheres of small planets with high mean molecular weight, and the capability to distinguish between the variability introduced by stellar activity and/or the planetary atmosphere will require high-resolution spectrographs in the upcoming extremely large telescopes.