Internal Heat and Energy Imbalance of Uranus

TL;DR

This study analyzes Uranus's energy budget over a full orbit, revealing ongoing global cooling, significant internal heat flux, and energy imbalances that are vital for understanding its climate and internal structure.

Contribution

It provides the first comprehensive measurement of Uranus's seasonal energy budget and confirms the presence of internal heat, resolving a long-standing debate.

Findings

Uranus emits more thermal energy than it absorbs from the Sun.

Significant seasonal variations influence Uranus's energy budget.

Global and hemispheric energy imbalances are identified and should inform future models.

Abstract

With its extreme axial tilt, radiant energy budget and internal heat of Uranus remain among the most intriguing mysteries of our Solar System. Here, we present the global radiant energy budget spanning a complete orbital period, revealing significant seasonal variations driven primarily by the highly variable solar flux. Despite these fluctuations, emitted thermal power consistently exceeds absorbed solar power, indicating a net energy loss and ongoing global cooling. Based on the seasonal variations of radiant energy budget, we determine a statistically significant internal heat flux. This finding resolves a long-standing debate over whether Uranus possesses internal heat. We also examine the energy budget of the weather layer by combining the internal heat with the radiant energies, revealing significant energy imbalances at both global and hemispheric scales. These global and hemispheric imbalances should be considered in theoretical and numerical models. The Uranus flagship mission, as recommended by the recent survey, will provide crucial observations to address more unresolved questions and advance our understanding of this enigmatic ice giant.