Pluto's atmosphere with ALMA: disk-resolved observations of CO and HCN, and first detection of HNC
Résumé
Following our detection of HCN(4-3) and CO(3-2) in 2015 (Lellouch et al. 2017), we pursued our exploration of Pluto's atmosphere with ALMA. On July 30, 2017, we obtained maps of these CO and HCN emissions, with a 96 x 54 mas beam providing some spatial resolution of the Pluto disk in the North-South direction. On April 27, 2017, we explored portions of the 256.1-259.1 and 271.9-273.8 GHz spectrum, searching for HNC, CH3CN, and H13CN in disk-averaged observations. The highlight of this search was the detection of the HNC(3-2) line at 271.98 GHz, which appears as a narrow emission with a 15 mJy contrast. This first identification of HNC in Pluto's atmosphere reinforces the similarity to Titan's upper atmosphere, where HNC has been also observed (Moreno et al. 2011). Data interpretation in terms of (i) the spatial distribution of CO and HCN emissions (ii) the HNC abundance/vertical distribution, including comparison with photochemical models, will be presented.