Presentation #415.02 in the session Giant Planet Atmospheres (iPosters).
The cause of the excessively high temperatures of the upper atmospheres of the outer planets has been an open question since the Voyager epoch. Observations of the H2 emission from the neutral thermosphere and the ionospheric H3+ emission provide a complete view of both the charged and the neutral components of their upper atmospheres. In the case of Uranus, the temperature has been steadily declining for almost 30 years, but still remains elevated. By obtaining observations of Uranus’ H2 and H3+ emission at the IRTF, and at Gemini as part of a Large & Long Term Program, we have been monitoring the response of Uranus’ upper atmosphere to the post-2007 equinox solar forcing in search of the anticipated seasonal trend reversal. Determining the seasonal phase lag of the trend reversal would yield the dissipative time constant of the Uranian upper atmospheric system, which in turn may provide insight into the process responsible for its unexplained heating. We report the results of observations we obtained during the 2021 apparition.
This research was supported by NASA grant NSSC18K0860.