When Voyager 2 flew past Uranus in 1986, the spacecraft detected a surprisingly low level of internal heat from the planet. Since then, scientists believed Uranus to be the odd one out in our solar system’s family of giant planets—the others being Jupiter, Saturn, and Neptune—who all tend to emit more heat than they absorb from sunlight.

Now, a new study suggests that scientists may have had the wrong idea about Voyager 2’s data: Uranus does have an internal heat source similar to its planetary siblings. For the study, published Monday in Geophysical Research Letters, researchers analyzed decades of archival data available on the ice giant, finding that Uranus emits 12.5% more internal heat than it absorbs from the Sun. 

That’s still considerably less heat than the other three giant planets, which emit more than 100% of the solar energy they receive. Nevertheless, the study demonstrates that Uranus doesn’t stray too far from scientists’ general understanding of how giant planets form and evolve. 

To reach this conclusion, the researchers analyzed data on Uranus’s global energy balance across one full orbit of the Sun, which takes 84 years. The team took this observational data and combined it with computational models, finding big seasonal swings driven by the planet’s wild changes in sunlight exposure. The new findings are consistent with an earlier paper about Uranus’s energy balance, published in Monthly Notices of the Royal Astronomical Society in May.

That said, neither study offers a clear answer as to why Uranus’s internal heat is much lower than the other gas and ice giants. Uranus may have had a “different interior structure or evolutionary history compared to the other giant planets,” the researchers noted in a statement. The study also found that Uranus’s energy levels change according to its 20-year-long seasons. These fluctuations, along with the planet’s heat budget, “provide observational constraints that can be used to develop theories of planetary formation for giant planets,” the study states. 

Thus, the paper both answers and raises questions about Uranus, which the researchers cite as a good reason for future NASA missions to investigate the icy planet further. 

“By uncovering how Uranus stores and loses heat, we gain valuable insights into the fundamental processes that shape planetary atmospheres, weather systems, and climate systems,” said Liming Li, study co-author and physicist at the University of Houston, in the release. “These findings help broaden our perspective on Earth’s atmospheric system and the challenges of climate change.”