The GAPS Programme at TNG XXXVIII. Five molecules in the atmosphere of the warm giant planet WASP-69b detected at high spectral resolution

TL;DR

This study used high-resolution spectroscopy to detect five molecules in the atmosphere of the warm giant exoplanet WASP-69b, revealing a potentially carbon-rich atmosphere with disequilibrium chemistry.

Contribution

First simultaneous detection of five molecules in a warm giant planet's atmosphere using high-resolution transmission spectroscopy.

Findings

Detected CH₄, NH₃, CO, C₂H₂, and H₂O at >3.3σ

No confident detection of HCN and CO₂

Indications of a carbon-rich, disequilibrium atmospheric chemistry

Abstract

The field of exo-atmospheric characterisation is progressing at an extraordinary pace. Atmospheric observations are now available for tens of exoplanets, mainly hot and warm inflated gas giants, and new molecular species continue to be detected revealing a richer atmospheric composition than previously expected. Thanks to its warm equilibrium temperature (963$\pm$18~K) and low-density (0.219$\pm$0.031~g cm$^{-3}$), the close-in gas giant WASP-69b represents a golden target for atmospheric characterization. With the aim of searching for molecules in the atmosphere of WASP-69b and investigating its properties, we performed high-resolution transmission spectroscopy with the GIANO-B near-infrared spectrograph at the Telescopio Nazionale Galileo. We observed three transit events of WASP-69b. During a transit, the planetary lines are Doppler-shifted due to the large change in the planet's radial velocity, allowing us to separate the planetary signal from the quasi-stationary telluric and stellar spectrum. Considering the three nights together, we report the detection of CH$_4$, NH$_3$, CO, C$_2$H$_2$, and H$_2$O, at more than $3.3\sigma$ level. We did not identify the presence of HCN and CO$_2$ with confidence level higher than 3$\sigma$. This is the first time that five molecules are simultaneously detected in the atmosphere of a warm giant planet. These results suggest that the atmosphere of WASP-69b is possibly carbon-rich and characterised by the presence of disequilibrium chemistry.