2025-07-14 ヒューストン大学
A study from University of Houston researchers showed Uranus’s energy levels change with its long seasons, which last about 20 years. This is likely caused by the planet’s off-center orbit and tilted spin. (Rendering credit Getty Images)
＜関連情報＞
- https://uh.edu/news-events/stories/2025/july/07142025-uranus-internal-heat-study.php
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL115660
天王星の内部熱流束とエネルギー不均衡 Internal Heat Flux and Energy Imbalance of Uranus
Xinyue Wang, Liming Li, Michael Roman, Xi Zhang, Xun Jiang, Patrick Fry, Cheng Li, Gwenael Milcareck, Agustin Sanchez-Lavega, Santiago Perez-Hoyos, Ricardo Hueso, Tristan Guillot …
Geophysical Research Letters Published: 14 July 2025
DOI:https://doi.org/10.1029/2025GL115660
Abstract
With its extreme axial tilt, Uranus’ radiant energy budget (REB) and internal heat flux remain among the most intriguing mysteries in our solar system. By combining observations with modeling, we present the global REB over a complete orbital period (1946–2030), revealing significant seasonal variations. Despite these fluctuations, the global average emitted thermal power consistently exceeds absorbed solar power, indicating a net energy loss. Assuming no significant seasonal variation in emitted power, we estimate an internal heat flux of 0.078 ± 0.018 W/m2 by analyzing the energy budget over one orbital period. The combination of internal heat and radiant energies indicates substantial global and hemispheric imbalances, with excesses or deficits exceeding 85% of emitted power at the hemispheric scale. These findings are crucial for understanding Uranus’ interior and atmosphere. A future flagship mission to Uranus would provide critical observations to address more unresolved questions of this enigmatic ice giant.
Key Points
- Analyses of Uranus’ global radiant energy budget (REB) spanning a complete orbital period (1946–2030) reveal significant seasonal variations
- A statistically significant internal heat flux of 0.078 ± 0.018 Wm−2 is determined from long-term investigations of Uranus REB
- Large energy imbalances at both global and hemispheric scales are suggested for Uranus’ weather layer
Plain Language Summary
The study of radiant energy budgets and internal heat is crucial in astronomy, planetary science, and atmospheric science, as it helps us understand planetary weather, climate dynamics, and the processes governing planetary formation and evolution. Uranus, with its extreme axial tilt and enigmatic energy balance, presents a particularly compelling case. In this study, we present the global-average radiant energy budget spanning a complete orbital period (1946–2030) based on observations and modeling, revealing significant seasonal variations driven primarily by Uranus’ highly variable solar flux. Despite these fluctuations, our results show that emitted thermal power consistently exceeds absorbed solar power, indicating a net energy loss. From these seasonal variations, we determine a statistically significant internal heat flux, resolving the long-standing debate on its magnitude. Furthermore, we analyze the energy budget of Uranus’ weather layer by integrating internal heat with radiant energies, uncovering substantial energy imbalances at both global and hemispheric scales. This is the first study to quantify seasonal energy imbalances on Uranus. Our findings provide critical insights into the planet’s thermal dynamics for future investigations, including those by a potential flagship mission to Uranus.
