Uranus is so weird. Its magnetic field doesn’t go through the center of the planet, it rotates on its side, and it is fairly featureless. Some of the peculiarities might be due to a colossal impact in its past. Still, they make it difficult to assess even simple properties like the length of a day on the planet. Now a new technique has improved original measurements from Voyager 2 in 1986.
The crucial aspect of the new method is the aurorae. Due to the misalignment between the rotational axis and magnetic field, these do not exist around the pole like on Earth or Jupiter. Despite the complexity, the team was able to use them to improve on the Voyager method by a factor of 1,000. The day on Uranus is 17 hours, 14 minutes, and 52 seconds, which is 28 seconds longer than Voyager’s estimate.
The team was able to create a better system of coordinates that will certainly be useful in the future when a new mission to the ice giant plant is approved.
“Our measurement not only provides an essential reference for the planetary science community but also resolves a long-standing issue: previous coordinate systems based on outdated rotation periods quickly became inaccurate, making it impossible to track Uranus’ magnetic poles over time,” lead author Laurent Lamy, from the Observatoire de Paris, said in a statement. “With this new longitude system, we can now compare auroral observations spanning nearly 40 years and even plan for the upcoming Uranus mission.”
Uranus’ aurorae snapped by Hubble across October 2022.
Image Credit: ESA/Hubble, NASA, L. Lamy, L. Sromovsky
This new measurement was only possible thanks to the long-term campaign of Uranus observations by the Hubble Space Telescope. Across more than 10 years, Hubble’s observations of aurorae on Uranus have provided the key data – not bad for a telescope about to turn 35!
“The continuous observations from Hubble were crucial,” says Lamy. “Without this wealth of data, it would have been impossible to detect the periodic signal with the level of accuracy we achieved.”
Uranus and Neptune have only been visited once, by Voyager 2. The spacecraft flew by them without stopping, so there is a lot that we do not know about these distant worlds. Research like this provides important new insights and helps prepare the road to the eventual return of a mission to the planet, ideally one that can stay in orbit long term, providing a new understanding of the planet and its moons.
The team’s paper has been published in the journal Nature Astronomy.
