Measuring Neptune's temperature maps and CO abundance with ALMA

Remote-sensing monitoring of Neptune has revealed temperature variations in the atmosphere of the planet ^[1,2,3,4] since the flyby of Voyager 2 ^[5]. These variations are not uniform in latitude or pressure level, with the Southern polar region and the stratospheric pressure levels showing higher levels of activity. In this work we present the analysis of ALMA observations of Neptune at the CO(3-2) line at 345.8GHz. These measurements were recorded in 2016 with a spatial resolution of about 0.37” on Neptune’s 2.24” disk. We find that this spectral range is sensitive to Neptune’s upper troposphere and lower stratosphere, probing between about 1 and 10^-3 bar.

We developed an MCMC retrieval methodology coupled to a pre-existing radiative transfer code ^[6] to derive Neptune’s temperature fields and constrain the atmospheric abundance of CO. We explored the correlation between both parameters by carrying out simultaneous retrievals to the temperature and CO abundance, both on disk-averaged and spatially-resolved data. We then explored the latitudinal variations of temperature and derived temperature maps of the planet. We compare these results with previous works in the literature, and discuss the latitudinal variability measured with ALMA.

 

[1] Orton et al. 2007, A&A 473, L5
[2] Lellouch et al. 2010, A&A 518, L152
[3] Fletcher et al. 2014, Icarus 231, 146–167
[4] Roman et al. 2022, Planet. Sci. J. 3:78
[5] Conrath et al. 1998, Icarus 135, 2, 501–517
[6] Moreno et al. 2017, A&A 608, L5