Uranus Is Making Its Own Heat todayheadline

A new study led by the University of Houston and an international team of planetary scientists has answered one of the longest-running mysteries in planetary science: Uranus does, in fact, have its own internal heat. Published in Geophysical Research Letters, the research uses data spanning an entire Uranian year (1946–2030) to show that the planet emits about 12.5 percent more energy than it absorbs from sunlight, resolving decades of conflicting evidence since Voyager 2’s flyby in 1986.

A Planet With An Energy Deficit

Uranus is often called the solar system’s most enigmatic planet. With an axial tilt of nearly 98 degrees, it experiences extreme seasonal swings, each lasting over 20 years. Yet despite these variations in sunlight, researchers found the emitted thermal radiation of Uranus to be essentially constant. The new analysis determined that:

• The planet emits 0.692 ± 0.014 W/m² of thermal energy, measured by Voyager and confirmed by later ground-based observations.
• It absorbs less solar energy, averaging 0.614 ± 0.012 W/m².
• This difference yields a statistically significant internal heat flux of 0.078 ± 0.018 W/m².

This flux represents about 12.5 percent of the solar power Uranus absorbs, a modest figure compared with Neptune, Jupiter, and Saturn, whose internal heat exceeds their absorbed sunlight. Still, it proves Uranus is slowly radiating leftover heat from its formation billions of years ago.

Seasonal Extremes And Energy Imbalances

By modeling the radiant energy budget over an entire 84-year orbit, the team also found dramatic imbalances between hemispheres. At the solstices, one hemisphere experiences nearly double its emitted energy as excess input, while the opposite side suffers deficits reaching almost 90 percent.

“The planet Uranus emits more heat than it gets from the Sun,” said first author Xinyue Wang. “This means it’s still slowly losing leftover heat from its early history, a key piece of the puzzle that helps us understand its origins and how it has changed over time.”

Such findings suggest powerful atmospheric circulation must transport energy from one hemisphere to the other, an idea supported by previous dynamical models but never before constrained with full-orbit data. For planetary scientists, this means Uranus’ weather systems are powered by more than just the sunlight it receives.

Why It Matters

Understanding internal heat flux is central to planetary formation theories. Unlike Earth, where radioactive decay drives most internal heat, giant planets release residual energy from their accretion and differentiation. The new measurements confirm that Uranus is cooling, but at a slower and weaker rate than Neptune, hinting at differences in their internal structure or evolutionary paths. As noted by the 2023–2032 Decadal Survey, a flagship orbiter mission to Uranus is now a top priority for NASA. Such a mission could finally reveal how this tilted ice giant redistributes heat and why it differs from its planetary siblings.

A Glimpse Beyond Uranus

The study also has broader implications. By refining methods to track planetary energy budgets, scientists can apply similar models to Neptune, exoplanets, and even Earth. Insights into how heat drives weather and circulation patterns help researchers interpret climates on worlds both near and far. For Earth science, comparisons with Uranus may sharpen understanding of energy imbalances driving climate change, as documented by NASA and the Intergovernmental Panel on Climate Change.

For now, Uranus continues to glow faintly with its ancient heat, a reminder that even the coldest-looking planets hide restless secrets within. The next spacecraft to orbit the planet may finally explain why Uranus, alone among the giants, radiates so little of what it holds inside.

Journal: Geophysical Research Letters. DOI: 10.1029/2025GL115660