Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
EPSC Abstracts
Vol. 14, EPSC2020-268, 2020
https://doi.org/10.5194/epsc2020-268
Europlanet Science Congress 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The long-term cooling of the upper atmosphere of Uranus

Henrik Melin1, Leigh Fletcher1, Tom Stallard1, Larry Trafton4, Emma Thomas1, Luke Moore2, Nahid Chowdhury1, and James O'Donoghue3
Henrik Melin et al.
  • 1School of Physics & Astronomy, University of Leicester, Leicester, UK
  • 2Boston University, USA
  • 3JAXA, Japan
  • 4University of Texas, Austin, USA

Abstract

 This molecular ion H3+ provides a really powerful tool with which we can remotely measure the ionospheric density and thermospheric temperature of the gas giants using near-infrared ground-based telescopes. These measurements show that the upper atmosphere of all four giant planets in our solar system are much hotter than solar input along can produce - this is known as the ‘energy crisis’ - and it is currently unclear from where this additional energy is sourced from. The two major candidates are the re-distribution of auroral Joule heating and the breaking of gravity waves generated in the turbulent lower atmosphere. Emission from H3+ has been observed from Uranus on a semi-regular intervals since 1992. We have previously shown that the upper atmosphere is subject to a remarkable long-term cooling, and has cooled from ~750 K in 1992 to 500 K in 2018, at a rate of ~8 K/year. This has important implications for the drivers of the elevated temperatures in the upper atmosphere, and may be related to the ever changing geometry between the offset magnetic field of Uranus the incoming  solar-wind. Here, we present the latest observations of H3+ emission from Uranus, obtained using the iSHELL instrument at the NASA Infrared Telescope Facility (IRTF) in October and November 2019. We explore any potential changes in the observed cooling, and discuss how these new observations fit within our current theories  of how the upper atmosphere of Uranus is heated.

 

 Figure 1: The long-term temperature (a) and density (b) evolution of the upper atmosphere of Uranus between 1992 and 2018. 

 

How to cite: Melin, H., Fletcher, L., Stallard, T., Trafton, L., Thomas, E., Moore, L., Chowdhury, N., and O'Donoghue, J.: The long-term cooling of the upper atmosphere of Uranus , Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-268, https://doi.org/10.5194/epsc2020-268, 2020.