Hubble Pinpoints Uranus' Rotation with Unmatched Precision

Explore Hubble

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This visual shows three panels that each show Uranus and dynamic aurora activity. The images were captured in October 2022 on the 8th, 10, and 24th respectively. Each image shows the planet with a strong blue hue and a visible white region. A faint ring is also visible around the planet in each image. Each image shows fuzzy blue/purple regions hovering over the planet in different locations to indicate the aurorae.

These images from the NASA/ESA Hubble Space Telescope showcase the dynamic aurora on Uranus in October 2022.

Credits:

ESA/Hubble, NASA, L. Lamy, L. Sromovsky

An international team of astronomers using the NASA/ESA Hubble Space Telescope has made new measurements of Uranus' interior rotation rate with a novel technique, achieving a level of accuracy 1,000 times greater than previous estimates. By analyzing more than a decade of Hubble observations of Uranus' aurorae, researchers have refined the planet's rotation period and established a crucial new reference point for future planetary research.

These images from the NASA/ESA Hubble Space Telescope showcase the dynamic aurora on Uranus in October 2022. These observations were made by the Space Telescope Imaging Spectrograph (STIS) and includes both visible and ultraviolet data. An international team of astronomers used Hubble to make new measurements of Uranus' interior rotation rate by analyzing more than a decade of the telescope's observations of Uranus' aurorae. This refinement of the planet's rotation period achieved a level of accuracy 1000 times greater than previous estimates and serves as a crucial new reference point for future planetary research.

ESA/Hubble, NASA, L. Lamy, L. Sromovsky

Determining a planet's interior rotation rate is challenging, particularly for a world like Uranus, where direct measurements are not possible. A team led by Laurent Lamy (of LIRA, Observatoire de Paris-PSL and LAM, Aix-Marseille Univ., France), developed an innovative method to track the rotational motion of Uranus' aurorae: spectacular light displays generated in the upper atmosphere by the influx of energetic particles near the planet's magnetic poles. This technique revealed that Uranus completes a full rotation in 17 hours, 14 minutes, and 52 seconds - 28 seconds longer than the estimate obtained by NASA's Voyager 2 during its 1986 flyby.

"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," explains Lamy. "With this new longitude system, we can now compare auroral observations spanning nearly 40 years and even plan for the upcoming Uranus mission."

This image of Uranus' aurorae was taken by the NASA/ESA Hubble Space Telescope on 10 October 2022. These observations were made by the Space Telescope Imaging Spectrograph (STIS) and includes both visible and ultraviolet data. An international team of astronomers used Hubble to make new measurements of Uranus' interior rotation rate by analyzing more than a decade of the telescope's observations of Uranus' aurorae. This refinement of the planet's rotation period achieved a level of accuracy 1000 times greater than previous estimates and serves as a crucial new reference point for future planetary research.

ESA/Hubble, NASA, L. Lamy, L. Sromovsky

This breakthrough was possible thanks to Hubble's long-term monitoring of Uranus. Over more than a decade, Hubble has regularly observed its ultraviolet auroral emissions, enabling researchers to produce magnetic field models that successfully match the changing position of the magnetic poles with time.

"The continuous observations from Hubble were crucial," says Lamy. "Without this wealth of data, it would have been impossible to detect the periodic signal with the level of accuracy we achieved."

Unlike the aurorae of Earth, Jupiter, or Saturn, Uranus' aurorae behave in a unique and unpredictable manner. This is due to the planet's highly tilted magnetic field, which is significantly offset from its rotational axis. The findings not only help astronomers understand Uranus' magnetosphere but also provide vital information for future missions.

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