Decades of data collected by the Hubble Space Telescope has given an international team of astronomers fresh insight into what’s going on with Uranus. A new analysis, published in Nature Astronomy, calculates the spin of one of our solar system’s most understudied planets with unprecedented precision.
A human-made object has visited the seventh planet from the Sun just once. On January 24, 1986, NASA’s Voyager 2 spacecraft conducted a flyby, gathering some of the most comprehensive data scientists have had access to when it comes to Earth’s distant neighbor. That included some oddities, such as the fact that Uranus’ magnetic field was both highly tilted and offset. By comparing measurements of that field, astronomers were able to estimate the planet’s rotation at 17 hours, 14 minutes, and 24 seconds.
However, there was a margin of error of 36 seconds built into that calculation. That may seem small, but as the astronomers noted in their new paper, it was enough that observers were no longer able to find the magnetic axis of the planet less than two years after Voyager 2’s visit.
That uncertainty was because giant planets such as Uranus pose unique problems for scientific observers. While Uranus is not technically a gas giant, as it has a solid core, it’s hard to see what’s actually going on through all that gas, as powerful winds rip through the thick atmosphere.
An attempt to re-analyze ultraviolet data collected by Voyager 2 in 2009 wasn’t able to improve the understanding of how fast Uranus was rotating. To solve the riddle, astronomers turned to the Hubble Space Telescope, which began capturing images of the planet’s ultraviolet auroras in 2011. Like the auroras that can be found here on Earth, such as the Northern Lights, Uranus’ are caused by particles striking the atmosphere and interacting with the magnetic field. More images were taken in the subsequent years, allowing for the observation of the spectacular light shows under different solar wind and magnetospheric conditions.
Analysis of the Hubble imagery, combined with the data collected by Voyager 2, allowed for a more exact calculation of Uranus’ rotation speed. What they found did indeed fall within the original margin of error: according to their calculations, Uranus is spinning at exactly 17 hours, 14 minutes, and 52 seconds. There’s still a margin of error, but it’s down to 0.036 seconds.
“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,” said Laurent Lamy, an astronomer at France’s Observatoire de Paris-PSL who led the research team, 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.”
The mission he’s referring to is an as-yet-unscheduled probe that was listed as a major priority for NASA in 2022 by the National Academies of Sciences, Engineering, and Medicine. That craft will be tasked with mapping Uranus’ gravitational and magnetic fields, a mission that will be easier thanks to this new discovery.
But (and with Uranus, there’s always a but), that mission exists purely on paper right now. NASA along with much of the federal government faces an uncertain future, so it’s uncertain when, or if, humans will once again poke around in that distant gassy wonder.
