Investigations of Neptune's Atmospheric Composition with ALMA

Tuesday, 15 December 2020
Lidiya Y Ahmed1, Conor A Nixon1 and Alexander E Thelen2, (1)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (2)USRA / NASA Goddard Space Flight Center, Greenbelt, MD, United States
Ground and space-based facilities currently serve as the primary means to study the composition and variation of the Ice Giant atmospheres, which remain poorly understood. Here, we present the analysis of archival hyperspectral data of Neptune collected by the Atacama Large Millimeter/submillimeter Array (ALMA) for flux calibration purposes during astrophysical observation campaigns. Neptune was observed frequently throughout the last decade. Archival observations exhibit clear spectroscopic detections of HCN and CO, and have the potential to enable the detection of further trace species such as HC3N, C3H4, and isotopes of C- and N-bearing species (such as HC15N, 13CO etc). We searched for spectral lines of gases not previously identified on Neptune such as HC3N, and gases only seen previously in the infrared (e.g. C3H4). We measured the spatial distribution of HCN as a function of time, and we present emission maps from HCN J=3-2 and J=4-3 transitions from ALMA archival data spanning 2012-2018. The results of these ALMA archival studies will be highly informative about the chemistry, composition, and dynamics of Neptune’s atmosphere.