On April 7, 2025, a rare cosmic event allowed scientists to peer deep into the atmosphere of Uranus. As the distant ice giant passed in front of a star 400 light-years away, astronomers captured a wealth of atmospheric data in what’s known as a stellar occultation.
The Uranus Stellar Occultation Campaign 2025 brought together over 30 astronomers across 18 professional observatories. Led by NASA’s Langley Research Center, the team capitalized on a fleeting, hour-long alignment visible only in parts of western North America. As Uranus moved between Earth and a distant star, its atmosphere subtly refracted the star’s light producing a light curve that scientists could analyze to decode the planet’s temperature, pressure, and density at various altitudes.
“We are able to measure the light curve and determine Uranus’ atmospheric properties at many altitude layers,” explained William Saunders, principal investigator at NASA Langley.
By charting how the star’s light dimmed as it entered and exited Uranus’ atmosphere, scientists could gain unprecedented insight into how energy moves through the planet’s atmospheric layers. This is particularly important for understanding why Uranus’ upper atmosphere is so inexplicably hot, despite being nearly 2 billion miles from the Sun.
With no solid surface and an atmosphere primarily composed of hydrogen, helium, methane, and ammonia, Uranus is a natural laboratory for studying storm dynamics and cloud formation minus the complexity of surface interactions.
The April event wasn’t NASA’s first attempt at tracking Uranus in this way. A test run in November 2024 involving telescopes in Japan, Thailand, and India — helped scientists calibrate equipment and refine predictions. These efforts proved crucial, improving the accuracy of Uranus’ position during the April event by 125 miles.
Emma Dahl, a postdoctoral scholar at Caltech said: “As scientists, we do our best work when we collaborate… These kinds of planetary atmospheres allow us to study cloud formation, storms, and wind patterns in isolation.”
While this was the most detailed observation of Uranus since Voyager 2’s flyby in 1986, it’s far from the last. The next bright stellar occultation involving Uranus is expected in 2031 and will involve a brighter star, allowing for even better observations.
NASA hopes to use airborne and potentially space-based observatories to build on this work and possibly even inform the design of future missions to this long-overlooked world.
