Exploring the atmosphere of GJ 1132 b with CRIRES+

TL;DR

This study used CRIRES+ to analyze the atmosphere of GJ 1132 b, aiming to detect specific molecules, but found no evidence of them, highlighting the challenges and capabilities of high-resolution spectroscopy for rocky exoplanets.

Contribution

First high-resolution spectroscopic analysis of GJ 1132 b's atmosphere with CRIRES+ establishing upper limits on key molecules.

Findings

No detection of H I, HCN, CH₄, or H₂O in the atmosphere.

CRISRES+ can set upper limits on atmospheric composition.

Highlights the need for high-resolution spectrographs on future telescopes.

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 H$_2$O in large enough quantities to match the HST observations. The proposed atmosphere detection, however was challenged by reanalysis of the same HST data by different teams. Recent JWST 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, CH$_4$, and H$_2$O 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, H$_2$-dominated atmosphere, although we can place upper limits for the volume mixing ratios of CH$_4$, HCN, and H$_2$O using injections tests and atmospheric retrievals. These retrieved upper limits show the capability of CRIRES+ to detecting chemical species in rocky exoplanets, if the atmosphere is H$_2$ 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.