High-resolution exploration of transiting sub-Neptunes’ atmospheres with NIRPS

Atmospheric characterization of smaller exoplanets has entered a new era with the capabilities of JWST and the latest high-resolution spectrographs such as NIRPS, in combination with HARPS on the ESO 3.6m at La Silla, which has started operations on April 1st, 2023. By the start of the EGU General Assembly 2024, the NIRPS consortium has scheduled 25 transits of more than 10 sub-Neptunes (< 3 REarth) not named TRAPPIST-1, and many more to come during the 725 total nights of NIRPS Guaranteed Time Observations (GTO).In this talk, we present an early overview of the high-resolution transmission spectroscopy analysis of those targets, looking for a wide range of atomic and molecular species both in infrared and in the visible, and compare those results with the latest JWST findings for those targets. We show that NIRPS observations lead to some of the most precise transmission spectra in the metastable helium region ever produced, strongly constraining this element's presence or lack thereof in the upper atmosphere of exoplanets.