Uranus temperature
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Understanding the Temperature of Uranus
Upper Atmosphere Temperature: Ultraviolet Spectrometer Observations
The upper atmosphere of Uranus, primarily composed of atomic and molecular hydrogen, exhibits a temperature of approximately 750 kelvins. This high temperature is inferred from solar and stellar occultations, which also reveal the presence of methane and acetylene in the lower atmospheric levels . The ultraviolet spectrum of Uranus' sunlit hemisphere is dominated by emissions from atomic and molecular hydrogen, known as electroglow emissions, which are likely excited by low-energy electrons . The high temperature and the density of hydrogen atoms suggest an extensive thermal hydrogen corona around Uranus, impacting the orbital lifetime of ring particles .
Effective Temperature: Infrared and Far-Infrared Observations
Infrared and far-infrared spectrophotometry have been pivotal in determining the effective temperature of Uranus. Observations in the 30-55 micron spectral range indicate an effective temperature of about 57.7 K, with a slight margin of error . This temperature is close to the solar equilibrium value, suggesting minimal contribution from an internal heat source . Further data from the Voyager infrared spectrometer and radiometer (IRIS) investigation confirm an effective temperature of 59.1 K, providing a more precise measurement .
Temperature Inversions: Stratospheric and Tropospheric Profiles
Uranus exhibits a temperature inversion in its lower stratosphere, where temperatures increase with altitude. This inversion is weaker than previously thought, with a brightness temperature difference of 0.8 K between 17.8 and 19.6 microns . The stratospheric temperature profiles derived from stellar occultations also show that Uranus' stratosphere is warmer than expected from radiative models, with a maximum temperature around the 8-microbar pressure level . This nonisothermal feature suggests significant atmospheric circulation or the presence of an optically thin aerosol layer .
Seasonal Variations: Radiative-Convective Models
Seasonal variations in Uranus' thermal structure are influenced by its unique axial tilt, causing large changes in insolation over its 84-year orbital period. Radiative-convective models predict that the effective temperature varies by about 5 K at the poles and 0.5 K at the equator throughout the orbit . These variations are driven by the relatively small flow of heat from Uranus' interior, which is insufficient to counterbalance the seasonal changes in solar heating .
Conclusion
The temperature of Uranus is characterized by a high upper atmospheric temperature of around 750 K, an effective temperature close to 58 K, and notable temperature inversions in the stratosphere. Seasonal variations further complicate the thermal structure, driven by the planet's extreme axial tilt. These findings underscore the complex and dynamic nature of Uranus' atmosphere, shaped by both external solar radiation and internal processes.
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