A day on Uranus is actually longer than we thought, Hubble Telescope reveals

New Analysis Refines Uranus Rotation Period Using Hubble Data

Astronomers have refined the Uranus rotation period, finding the ice giant planet takes slightly longer to complete a single spin. A new examination of Hubble Space Telescope data, accumulated over a decade, indicates that Uranus requires 17 hours, 14 minutes, and 52 seconds for one full rotation. This updated measurement is 28 seconds greater than the previous estimate from NASA’s Voyager 2 mission nearly four decades prior.

Voyager 2’s Initial Estimate

In January 1986, Voyager 2 marked a milestone as the first and only spacecraft to explore Uranus. Data from this flyby allowed astronomers to calculate the rotation period of the pale turquoise planet at 17 hours, 14 minutes, and 24 seconds. This initial estimate was derived from radio signals emanating from Uranus’s auroras and direct measurements of its magnetic field. This figure became foundational for establishing coordinates and mapping the surface of this enigmatic world. However, a recent study suggests that some of these maps may require revision.

Challenges with Previous Uranus Data

The original estimate, based on Voyager 2’s data, contained inherent uncertainties that resulted in a 180-degree error in Uranus’s longitude. This discrepancy led to the orientation of its magnetic axis becoming “utterly lost” within mere years following the spacecraft’s passage. Consequently, coordinate systems reliant on the outdated rotation period rapidly lost their accuracy, as highlighted by the research.

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Hubble’s Decade-Long Observation

To address this issue, an astronomical team, spearheaded by Laurent Lamy from the Paris Observatory, monitored the movement of Uranus’s auroras using Hubble Space Telescope data. The data spanned from 2011 to 2022. By observing the progression of these luminous displays for over a decade, the researchers successfully pinpointed the planet’s magnetic poles with greater precision. This, in turn, allowed for a more accurate determination of its rotational period.

Importance of Continuous Hubble Data

“The sustained observations from Hubble were indispensable,” Lamy stated. “Without this extensive collection of data, discerning the periodic signal with the level of precision we achieved would have been unattainable.”

Broader Applications for Rotation Measurement

Researchers indicate that this method can now be employed to ascertain the rotation rate of any celestial body possessing a magnetic field and auroras. This applies not only within our solar system but also to exoplanets and other distant worlds.

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Implications for Future Uranus Missions

The updated estimate of Uranus’s rotation period offers a significantly more dependable coordinate system for the ice giant. Scientists anticipate this system to remain accurate for decades, until future space missions can gather even more refined data. According to the study, this enhanced estimate may prove valuable in planning forthcoming missions to Uranus, particularly in designing orbital paths and selecting suitable sites for atmospheric entry, Lamy and his team noted in their published findings.

Publication Details

The details of this research are available in a paper published (April 7) in the journal Nature Astronomy.