On April 7, Uranus passed in front of a distant star 400 light-years away, giving NASA scientists a rare space opportunity to study the distant icy giant.
During the hour-long event, called a stellar eclipse, Uranus’ atmosphere refracted the star’s light, diminishing it before blocking it completely. Although counter-intuitive, the dim light made it possible to illuminate aspects of Uranus that are normally difficult to see.
30 astronomers from 18 observatories across North America observed the eclipse. The researchers then used the data from the observation to create an irradiance curve that shows how starlight changed over time. From this curve, scientists can derive key information about Uranus’ stratosphere, including temperature, density, and pressure at different altitudes.
“NASA will use the observations of Uranus to determine how energy moves in the atmosphere and what causes the unexplained heating of the upper layers,” said NASA planetary scientist William Saunders in a press release. “Others will use this data to measure Uranus’ rings, the turbulence of its atmosphere, and its precise orbit around the Sun.”
Despite being nearly 2 billion kilometers away from the Sun, Uranus’s upper atmosphere is hotter than physics predicts. The light curve may provide some explanation.
This is the first time that NASA has organized such a large joint observation of a Uranian eclipse, the report said. The team was able to make a test run of the observations in November 2024, when they recorded a dimmer eclipse of Uranus using telescopes in Asia.
These observations helped to pinpoint the time of the eclipse and update the position of Uranus by about 125 miles (202 kilometers), which may not seem like much unless you’re trying to point multiple telescopes at the same moving target 2 billion miles (3.22 billion kilometers) from the opposite end of the world.
In addition to Uranus’ strange and turbulent atmosphere, this event also provided data on the planet’s ring system and its precise orbit around the Sun. This is more important than it seems: The first and only time a spacecraft flew by Uranus was Voyager 2 in 1986, and we still don’t know the planet’s position in space to within 100 miles.
Uranus has 13 known rings, 27 satellites, and many more mysteries. It consists mainly of hydrogen, helium, water, ammonia, and methane. The planet is classified as an ice giant because of the strange chemical cocktail that forms its interior. Imagine cold, gaseous slush with gusty winds and storms.
NASA is already looking forward to the next great eclipse of Uranus in 2031, which will be accompanied by an even brighter background star. This may mean that next time there will be airborne or even space-based observations that will help scientists better understand our local eccentric – a tilted planet with mysterious rings, Shakespearean moons, and many other secrets yet to be revealed.
