Hubble Telescope observations reveal that a day on Uranus is longer than previously thought. The spacecraft took nearly four decades to confirm the planet’s rotation period, but new analysis of Hubble Space Telescope data collected between 2011 and 2022 suggests that it actually takes 17 hours, 14 minutes, and 52 seconds for Uranus to complete a full rotation. This is 28 seconds longer than the estimated 17 hours, 14 minutes, and 24 seconds provided by NASA’s Voyager 2 spacecraft in 1986.
The initial estimate was based on radio signals emitted by Uranus’ auroras and magnetic field measurements. However, this led to a significant error in calculating coordinates on the planet’s surface, causing the orientation of its magnetic axis to become unreliable within just a couple of years after the Voyager 2 flyby.
To resolve this issue, astronomers tracked the motion of Uranus’ auroras using Hubble Space Telescope data and precisely pinpointed the planet’s magnetic poles. This allowed them to estimate the rotational period with greater accuracy.
The approach used in this study can now be applied to determine the rotation rate of any celestial object with a magnetic field and auroras, including exoplanets. The updated estimate provides a more reliable coordinate system for Uranus and is expected to remain accurate for decades until future missions offer even more refined data.
This research has implications for planning future missions to Uranus, particularly in defining orbital tours and selecting suitable atmospheric entry sites.
Source: https://www.space.com/the-universe/uranus/a-day-on-uranus-is-actually-longer-than-we-thought-hubble-telescope-reveals