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Measuring Neptune’s Stratospheric Winds Using ALMA

Presentation #212.18 in the session “Giant Planets, Exoplanets and Systems”.

Published onOct 03, 2021
Measuring Neptune’s Stratospheric Winds Using ALMA

Neptune exhibits some of the fastest winds in the solar system. The visit by Voyager 2 in 1989 allowed for some estimation of zonal wind speeds using cloud tracking, which ranged from 200 to 700 m s-1. However, the altitudes of clouds can not be constrained through cloud tracking methods alone, and so ambiguities on the motion of the atmosphere at different pressure levels remain. The Atacama Large Millimeter/submillimeter Array (ALMA) allows for the direct measurement of stratospheric winds through the Doppler shifts of molecular rotational transition lines. Emission from different molecules is concentrated in distinct regions of Neptune’s atmosphere, allowing for the first ever direct measurement of atmospheric winds at varying pressure levels. Observations from 2016 were analyzed to derive Doppler winds from two molecular lines: HCN J=4-3 (354.5 GHz) at ~3 mbar, and CO J=3-2 (~345.8 GHz) at ~10 mbar. Our analyses of derived HCN wind speeds agrees with previous cloud tracking measurements of retrograde motion at the equator. We will compare the HCN winds at the equator and higher latitudes to those derived from CO measurements at lower altitudes. Understanding the winds at different pressure levels is the first step towards building a vertical wind profile and a better understanding of Neptune’s atmospheric dynamical behavior.

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