Uranus was always seen as a tilted, distant, and kind of boring world. Scientists used to think it was a planetary dud, a cold world that refused to glow with leftover heat from its formation like its gassy cousins, Jupiter and Saturn.
But it turns out we were wrong.
Uranus actually has quite a bit of leftover heat. According to a blockbuster new study published in Geophysical Research Letters, the seventh planet is emitting more heat than it receives from the Sun. In fact, it’s bleeding energy into space — evidence that it’s still shedding heat from its formation.
You Met Me at a Weird Time
Back in 1986, NASA’s Voyager 2 zipped past Uranus for the first and only time. When the data came back, it was puzzling. Unlike Jupiter, Saturn, and Neptune, Uranus didn’t seem to be giving off much internal heat. That went against everything we thought we knew.
When gas giants form, they’re initially hot. They gobble up gas and dust in the chaos of a young solar system, and then slowly cool down over billions of years, releasing heat. Uranus didn’t seem to do that. Voyager 2 showed a world that just didn’t seem to give off heat.
You’d be tempted to leave it at “Weird, but okay.” But scientists don’t think that way. Now, almost 40 years later, they went back to the data. They had reinforcements: modern computer models, new telescope observations, and one big idea — maybe Uranus’s energy budget changes with its seasons. Maybe, just maybe, we caught Uranus at a weird time when we looked at it.
Strange Seasons
Uranus doesn’t have normal seasons. It’s tipped on its side — 97.7 degrees, like it’s lying down. Each pole spends about 20 years soaking in sunlight, then plunges into 20 years of darkness.
Xinyue Wang, the first author on the paper and a former doctoral student at the University of Houston dug deep into historical and modern observations covering most of a full Uranian year — about 84 Earth years. They tracked how much solar energy the planet absorbed and how much heat it gave off.
The researchers found that the thermal output isn’t constant, it changes with the seasons. Basically, the amount of sunlight Uranus absorbs and reflects varies wildly depending on its tilt and position in orbit. During parts of the year, the planet is releasing far more energy than it takes in. During others, it’s nearly balanced.
They found that overall, Uranus gives off 12.5% more heat than it absorbs via sunlight. This is lower compared to fluxes of upwards of 100% measured for Jupiter, Saturn and Neptune. It’s low, but it’s giving off heat nonetheless.
“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,” she explained.
Worth a Visit
Uranus’s internal heat has been a missing puzzle piece for decades. Without it, atmospheric models failed to explain some weird behaviors like strange wind patterns and bizarre cloud activity. Now, with this new number in hand, researchers can start tweaking those models to better simulate how weather and circulation work on the ice giants.
But it’s still not clear where this heat is coming from.
We don’t know the exact structure of Uranus’s interior. We don’t know what its seasons do to its cloud chemistry or wind belts. And we don’t know how its energy budget varies at different latitudes. Right now, much of the data we have comes from a flyby 30 years ago.
But the study could have implications for space exploration. In 2022, the National Academies named a Uranus orbiter and probe mission as NASA’s top planetary science priority for the decade. This heat discovery strengthens that case.
Unlike Mars or Jupiter, Uranus remains practically untouched. Yet it’s an utterly unique world: tipped sideways, cloaked in frigid clouds, and boasting a bizarre magnetic field that doesn’t even pass through the planet’s center. Its moons may harbor underground oceans. Its faint rings could tell us how planets form. And now we know it leaks internal heat — hinting at mysteries deep inside.
A Mission with Challenges
A flagship orbiter and probe could finally unravel how ice giants work, filling in the massive blind spot in our understanding of planetary formation, atmospheric dynamics, and magnetic evolution.
But flagship missions aren’t cheap, and the current Trump administration is defunding NASA and science in general.
Currently, the mission is still in the pre-Phase A stage, meaning no spacecraft exists yet, and funding is only trickling in. With mounting budget pressure across NASA, and fierce competition from lunar, Mars, and asteroid missions, Uranus could be delayed — or even sidelined.
If it launched, it won’t be before the 2030s. Ideally, it would orbit Uranus, deploy atmospheric instruments, and study its moons, rings, and interior in unprecedented detail. Thanks to this new study, we now have an even better reason to go.
The study was published in Geophysical Research Letters.
