Measurements made by the Voyager 2 spacecraft during its flyby of Uranus in 1986 found warm stratospheric and hot thermospheric temperatures that cannot be explained by solar heating alone. This contributes to what has become known as the “giant planet energy crisis”: there is a fundamental lack of understanding of the energy balance of the giant planets in the solar system. Uranus has the coldest stratospheric temperatures, the hottest thermospheric temperatures at some altitudes, and yet the weakest internal heat flux of all four giant planets. Moreover, the Voyager 2 temperature profiles are at odds with the many contemporaneous Earth-based stellar occultation observations. This unresolved tension impedes efforts to compare atmospheres in the solar system to one another and to exoplanet atmospheres.
In this dissertation, I present an investigation into the upper atmospheric temperatures of Uranus using archival Earth-based stellar occultation observations. I begin with an overview of planetary atmospheres and remote-sensing measurements of Uranus in Chapter 1. In Chapter 2, I derive and explain how stellar occultations are predicted, observed, processed, and analyzed, emphasizing my contributions. Chapter 3 describes how I validated these techniques on an archival Mars occultation. In Chapter 4, I present the results of comparing the Voyager 2 measurements to 26 archival Earth-based stellar occultations by Uranus. In Chapter 5, I present new temperature profiles from reprocessing these 26 occultations and a new one-dimensional atmospheric model based thereon. Chapter 6 outlines a low-Earth orbit mission concept to observe many new stellar occultations. Chapter 7 contains conclusions and summaries.
My primary finding is that the lower thermosphere of Uranus is much cooler than reported by Voyager 2. I find that the mesopause is likely higher in altitude than previously believed and the stratosphere of Uranus has a nearly isothermal section, in alignment with the other giant planets. My new atmospheric model suggests Uranus has a significant source of heat dissipation in the stratosphere, which might be supplied by gravity waves. This work can contribute to planning for any Uranus Orbiter and Probe mission by helping to revise Uranus’ representative temperature profile and improving our understanding of Uranus’ energy balance.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/49051 |
| Date | 26 June 2024 |
| Creators | Saunders, William R. |
| Contributors | Withers, Paul G. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial-ShareAlike 4.0 International, http://creativecommons.org/licenses/by-nc-sa/4.0/ |
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