The Hubble Space Telescope has revealed that Uranus has a longer day than we thought
A new analysis of over ten years of data from the Hubble Space Telescope has yielded an updated measurement of Uranus’ rotation period. According to this fresh research, Uranus takes precisely 17 hours, 14 minutes, and 52 seconds to complete a full spin on its axis—28 seconds longer than the figure estimated by NASA’s Voyager 2 mission nearly forty years ago.
Voyager 2 made history in January 1986 as the first—and still the only—spacecraft to fly by Uranus. Based on its observations, scientists previously calculated the planet’s rotation period to be 17 hours, 14 minutes, and 24 seconds. This figure came from tracking radio emissions linked to Uranus’ auroras and analyzing its magnetic field. For decades, this estimate served as the standard for mapping the planet and establishing coordinate systems. However, the latest study suggests that this foundational measurement might have led to long-standing inaccuracies.
The original rotation period estimate had significant limitations that introduced notable errors over time. According to researchers, this led to a drift of nearly 180 degrees in Uranus’ longitudinal coordinates, making it increasingly difficult to accurately locate the planet’s magnetic features. Within a few years of Voyager 2’s flyby, the planet’s magnetic axis had essentially become untraceable, rendering previously used coordinate systems unreliable.
To correct this, an international team led by Laurent Lamy of the Paris Observatory turned to Hubble Space Telescope data collected from 2011 through 2022. By tracking the motion of Uranus’ auroras across this extended period, the researchers managed to identify the location of the magnetic poles and, from that, determine a much more accurate rotational period. Lamy emphasized the importance of Hubble’s continuous monitoring, noting that without this long-term dataset, detecting the planet’s periodic signals with such precision would have been impossible.
This refined technique not only improves our understanding of Uranus but also provides a powerful tool for measuring the rotation of other celestial bodies that possess magnetic fields and auroras. This could include planets beyond our solar system, offering valuable insights into their magnetic and atmospheric dynamics.
The revised rotational period delivers a more dependable coordinate system for Uranus—one expected to remain valid for decades. This improvement is especially significant for future space missions targeting the distant ice giant. According to the study, it could play a crucial role in determining accurate orbital paths and selecting ideal atmospheric entry points for spacecraft exploration.
