  The hot Neptune desert, a distinct lack of highly irradiated planets in the
size range of Neptune, remains one of the most intriguing results of exoplanet
population studies. A deeper understanding of the atmosphere of exoplanets
sitting at the edge or even within the Neptune desert will allow us to better
understand if planetary formation or evolution processes are at the origin of
the desert. A detection of sodium in WASP-166b was presented previously with
tentative line broadening at the 3.4 sigma with the HARPS spectrograph. We
update this result with two transits observed with the ESPRESSO spectrograph,
confirming the detection in each night and the broadened character of the line.
This result marks the first confirmed resolved sodium detection within the
Neptune desert. In this work, we additionally highlight the importance of
treating low-SNR spectral regions, particularly where absorption lines of
stellar sodium and planetary sodium overlap at mid-transit - an important
caveat for future observations of the system.
