Decades of data collected by the Hubble Space Telescope have provided an international team of astronomers with groundbreaking insights into the enigmatic planet, Uranus. A recent analysis published in Nature Astronomy offers an unprecedentedly precise calculation of the spin of one of our solar system’s most understudied planets. Despite being the seventh planet from the Sun, Uranus has only been visited once by a human-made object.
On January 24, 1986, NASA’s Voyager 2 spacecraft made its historic flyby of Uranus, gathering some of the most comprehensive data available about this distant neighbor of Earth. During this mission, scientists noted some peculiarities, including the highly tilted and offset nature of Uranus’ magnetic field. By analyzing measurements of this magnetic field, astronomers estimated the planet's rotation period to be approximately 17 hours, 14 minutes, and 24 seconds. However, this calculation came with a margin of error of 36 seconds.
While a margin of error may seem minor, it proved significant enough that astronomers were unable to locate the planet's magnetic axis less than two years after the Voyager 2 mission. This uncertainty arises from the unique challenges posed by giant planets like Uranus. Although Uranus is not classified strictly as a gas giant due to its solid core, observing the planet's internal dynamics is complicated by powerful winds that sweep through its thick atmosphere.
Attempts to re-analyze ultraviolet data captured by Voyager 2 in 2009 did not yield improved insights into Uranus’ rotation speed. To tackle this scientific puzzle, astronomers shifted their focus to the Hubble Space Telescope, which began capturing images of the planet's ultraviolet auroras in 2011. Similar to the Northern Lights seen on Earth, Uranus' auroras are generated by particles colliding with the atmosphere and interacting with the planet's magnetic field.
Over the following years, Hubble gathered more images, allowing researchers to observe Uranus’ spectacular auroras under varying solar wind and magnetospheric conditions. By analyzing this Hubble imagery alongside the data collected by Voyager 2, astronomers were able to refine their calculations of Uranus’ rotation speed. Their findings indicated that Uranus spins at exactly 17 hours, 14 minutes, and 52 seconds, bringing the margin of error down to an impressive 0.036 seconds.
Laurent Lamy, an astronomer at France’s Observatoire de Paris-PSL and the leader of the research team, emphasized the significance of their measurement. “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,” he stated. “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 Lamy refers to is a yet-to-be-scheduled probe that was identified as a major priority for NASA in 2022 by the National Academies of Sciences, Engineering, and Medicine. This spacecraft will be tasked with mapping the gravitational and magnetic fields of Uranus, a mission that will be significantly aided by the recent discoveries made using Hubble data. However, it’s important to note that this mission currently exists only on paper. With NASA and much of the federal government facing an uncertain future, the timeline for when humans will once again explore this distant, gassy wonder remains uncertain.
