Temporal observations of HCN on Neptune’s atmosphere with ALMA

Previous ground and space-based observations have revealed a substantial amount of atmospheric activity and variability in the Ice Giant, Neptune. However, there are still many uncertainties about Neptune’s atmospheric composition and photochemistry. Here, we present new time-series maps of Neptune’s atmosphere from archival hyperspectral data collected by the Atacama Large Millimeter/submillimeter Array (ALMA) to investigate the temporal variability of its atmospheric composition. Archival observations exhibit clear spectroscopic detections of HCN, which is a potential tracer of Neptune’s stratospheric circulation. We show the spatial distribution of HCN emissions using the J=3-2 and J=4-3 transitions of HCN from ALMA archival data spanning 2012-2018. The results of these ALMA archival studies will provide new information about Neptune’s atmospheric circulation that can be used to plan future observations, and can be used to constrain models of the primordial composition, present-day chemistry, and dynamics of its atmosphere.