Tropospheric composition and circulation of Uranus with ALMA and the VLA

Tropospheric composition and circulation of Uranus with ALMA and the VLA

Molter, Edward M. (University of California)
de Pater, I. (TU Delft Astrodynamics & Space Missions; University of California)
Luszcz-Cook, Statia (Columbia University; American Museum of Natural History)
Tollefson, Joshua (University of California)
Sault, Robert J.
Butler, Bryan (National Radio Astronomy Observatory)
De Boer, David (University of California)

2021

We present Atacama Large Millimeter/submillimeter Array (ALMA) and Very Large Array (VLA) spatial maps of the Uranian atmosphere taken between 2015 and 2018 at wavelengths from 1.3 mm to 10 cm, probing pressures from ~1 to ~50 bar at spatial resolutions from 0 1 to 0 8. Radiative transfer modeling was performed to determine the physical origin of the brightness variations across Uranus's disk. The radio-dark equator and midlatitudes of the planet (south of ~50°N) are well fit by a deep H2S mixing ratio of 8.7+3.1- 1.5 ×10- 4 ( 37+13-6 × solar) and a deep NH3 mixing ratio of 1.7+0.7-0.4 ×10-4 ( 1.4+0.50.3× solar), in good agreement with models of Uranus's disk-averaged spectrum from the literature. The north polar region is very bright at all frequencies northward of ~50°N, which we attribute to strong depletions extending down to the NH4SH layer in both NH3 and H2S relative to the equatorial region; the model is consistent with an NH3 abundance of 4.7+2.1- 1.8 ×10-7 and an H2S abundance of <1.9×10-7 between ~20 and ~50 bar. Combining this observed depletion in condensible molecules with methane-sensitive near-infrared observations from the literature suggests large-scale downwelling in the north polar vortex region from ~0.1 to ~50 bar. The highest-resolution maps reveal zonal radio-dark and radio-bright bands at 20°S, 0°, and 20°N, as well as zonal banding within the north polar region. The difference in brightness is a factor of ~10 less pronounced in these bands than the difference between the north pole and equator, and additional observations are required to determine the temperature, composition, and vertical extent of these features.

http://resolver.tudelft.nl/uuid:098fc56c-adcb-4b31-b348-d5262c4ed75d

https://doi.org/10.3847/PSJ/abc48a

Planetary Science Journal, 2 (1)

Institutional Repository

journal article

© 2021 Edward M. Molter, I. de Pater, Statia Luszcz-Cook, Joshua Tollefson, Robert J. Sault, Bryan Butler, David De Boer