While it is relatively easy to know the speed of rotation of a terrestrial planet (Earth, Mars, Mercury, Venus), it becomes more difficult when it comes to a giant planet (Jupiter, Saturn, Neptune, Uranus).
This difficulty is due to its atmosphere, which masks the heart of the planet.
A team of researchers at Paris Observatory have found a new method for determining the rotation speed of Uranus with 1000 times greater accuracy, and it turns out that it rotates less quickly than we thought.
Until now, measurements were based on data obtained by the Voyager 2 spacecraft in 1986. At that time, the speed was calculated on the basis of data relating to Uranus’ magnetic field. The current method uses the aurorae observed in the ultraviolet by the Hubble Space Telescope. These data make it possible to find the position of the magnetic poles and deduce the planet’s internal rotation.
The LTE has contributed to the implementation of this measure by making available an ephemeris calculation tool that can be used to process data recorded over the long term, both from Voyager 2 and Hubble.
This new method opens up new fields for research into planetology and exoplanet-star systems, and the increased precision of the ephemeris will be essential for preparing new space missions to Uranus, which will in turn provide new data.
This discovery led to the publication of an article in the journal Nature Astronomy on 7 April 2025. You can find the Paris Observatory press release and the link to the article.
