In a dazzling leap forward for planetary science, an international team of astronomers has redefined what we know about Uranus—specifically, how fast it spins. Using a novel technique powered by over a decade of ultraviolet data from the NASA/ESA Hubble Space Telescope, researchers have determined the planet’s interior rotation period with astonishing precision. This breakthrough not only rewrites our understanding of Uranus’ internal mechanics but also lays a crucial scientific foundation for future exploratory missions to this icy enigma.
The research, led by Laurent Lamy of the Observatoire de Paris-PSL and Aix-Marseille University in France, has achieved a feat previously considered nearly impossible: measuring Uranus’ interior rotation rate to within a thousand times the accuracy of earlier estimates.
And how did they do it? Not with landers or seismic sensors—but by watching the aurorae dance.
Cracking the Code of a Sideways Spinning Giant
Measuring a planet’s rotation might seem straightforward. After all, we measure Earth’s daily spin with a simple clock. But for distant gas and ice giants like Uranus, whose surfaces are obscured by thick, swirling clouds and whose magnetic fields are bizarrely misaligned, things get tricky.
Very tricky.
Uranus spins on its side—almost literally. Its axis is tilted at about 98 degrees, which makes its seasons and magnetic interactions uniquely complex. Worse, unlike planets with strong visible surface features, Uranus hides any clear rotational signals under a pale blue cloak of haze.
NASA’s Voyager 2 flyby in 1986 provided the first estimate of the planet’s rotation, clocking it at about 17 hours and 14 minutes. But over time, that estimate has proven insufficient, particularly for accurately tracking the position of Uranus’ shifting magnetic poles. For decades, scientists have known the planet’s magnetosphere doesn’t follow the rules—and now, thanks to this new research, they know why.
Following the Auroral Breadcrumbs
Lamy and his team turned to the aurorae—brilliant ultraviolet light shows that shimmer near the planet’s magnetic poles when charged solar particles slam into its upper atmosphere. On Earth, we know these phenomena as the northern and southern lights. On Uranus, they’re far more mysterious.
What makes Uranus’ aurorae so special is their unpredictability. Unlike the consistent patterns seen on Earth, Jupiter, or Saturn, Uranian aurorae are chaotic. The planet’s magnetic field is not only tilted 59 degrees from its rotational axis, but also significantly offset from the planet’s center. It’s a geometric oddity that has stumped researchers for decades.
But therein lay the solution.
Using ultraviolet images captured by Hubble over more than ten years, the researchers tracked the movement of these aurorae across the planet’s disc. By aligning the timing of these light emissions with models of the magnetic field, they teased out a consistent, repeating signal.
That signal turned out to be Uranus’ true interior rotation rate: 17 hours, 14 minutes, and 52 seconds—exactly 28 seconds longer than Voyager’s initial estimate.
This may seem like a small correction, but it’s an enormous leap in precision. The new figure provides an essential “longitude zero”—a fixed reference point for tracking the magnetosphere and planning future missions. Without it, the planet’s magnetic coordinates drift over time, making long-term studies nearly impossible.
A New Clock for Uranus—and a Map for the Future
“This measurement not only provides an essential reference for the planetary science community but also resolves a long-standing issue,” said Lamy in a statement. “Previous coordinate systems based on outdated rotation periods quickly became inaccurate, making it impossible to track Uranus’ magnetic poles over time.”
With this new rotational clock, scientists can now align decades of auroral data—from Voyager’s snapshot to Hubble’s long-term surveillance—and anticipate how the planet’s magnetic field will evolve. It’s like upgrading from a sundial to an atomic clock.
The timing couldn’t be better. The U.S. National Academies’ Planetary Science Decadal Survey recently prioritized a Uranus Orbiter and Probe mission concept, aiming to explore the ice giant’s atmosphere, magnetosphere, moons, and rings in depth. That mission could launch in the 2030s—and thanks to this discovery, it will arrive with a detailed roadmap already in hand.
The Hubble Legacy: Watching a World Over Decades
None of this would have been possible without the unique observational capabilities of the Hubble Space Telescope. Unlike Earth-based observatories, which must contend with atmospheric interference, Hubble has had an unobstructed ultraviolet view of Uranus for over a decade—providing a consistent, long-term data stream that made this discovery possible.
“The continuous observations from Hubble were crucial,” Lamy emphasized. “Without this wealth of data, it would have been impossible to detect the periodic signal with the level of accuracy we achieved.”
This is yet another testament to Hubble’s enduring scientific legacy. Launched in 1990, the telescope continues to deliver critical insights into everything from star formation to dark energy—and, as we now know, the strange spin of distant planets.
Why Uranus Matters
Uranus is often overlooked in favor of flashier neighbors like Saturn and Jupiter, or the romantic mystique of Neptune. But planetary scientists argue that Uranus is exactly the kind of world we need to understand better. With a composition of icy materials and gases, it represents a class of exoplanets known as “ice giants” that are increasingly common in other star systems.
Yet we know shockingly little about it.
Uranus has at least 27 moons, a system of thin, dark rings, and an interior that may contain exotic phases of water and ammonia under extreme pressure. Understanding how such a world forms and behaves could unlock secrets not just of our own solar system, but of countless others.
This discovery—a deceptively precise measurement of a planet’s spin—is more than just a number. It’s a key that unlocks new scientific potential, opens doors to exploration, and reaffirms humanity’s ability to probe the universe with patience, ingenuity, and a bit of cosmic curiosity.
So, what’s next?
As the scientific community prepares to send a new generation of spacecraft to Uranus, this breakthrough offers both inspiration and instruction. By listening carefully to the faint whisper of aurorae, astronomers have finally tuned into Uranus’ heartbeat.
And with this rhythm now understood, we’re ready to dance closer to one of the most elusive planets in our celestial neighborhood.
Reference: L. Lamy et al, A new rotation period and longitude system for Uranus, Nature Astronomy (2025). DOI: 10.1038/s41550-025-02492-z