It is only very recently that we have been able to confirm how fast Saturn rotates on itself. For a long time, astronomers had trouble estimating it. We now know where the difficulty came from.
Determining the length of the day on Saturn has been a puzzle for scientists. The mystery was only solved very recently, in 2019, when astronomers and astrophysicists determined that it took this planet 10 hours, 33 minutes and 38 seconds to rotate around itself (they were able to verify this thanks to its rings). But it took until February 2022 to announce a new discovery, which helps to understand why it had been so difficult to come to a measurement for decades.
It is a mechanism described as ” unpublished “, at the origin of enormous planetary auroras, which has just been identified, reportedthe WM Keck Observatory on February 7. A study was also published in Geophysical Research Letters. ” We observed Saturn’s aurora borealis in infrared using the WM Keck Observatory in Mauna Kea, [sur l’île d’]Hawaii, during the months of June, July and August 2017 “, say the scientists.
Winds swirling through the atmosphere… and disrupting the magnetic field
It’s in the upper atmosphere, more than 1000 kilometers from the Hexagon of Saturn (circling clouds above its north pole) that winds could be observed, moving at more than 3,000 kilometers per hour, above the planet’s poles. In doing so, they disrupt Saturn’s magnetic field and change its auroras.
” This explains why Saturn’s day length has been difficult to measure for decades! », comment planetary scientist James O’Donoghue on Twitter, who took part in the study. Because we used to try to look at how fast Saturn’s magnetic field rotated to find out the length of the day.
On most of the planets studied (including the Earth), the auroras are formed from currents that enter the atmosphere, from the magnetosphere (on Earth, it is the result of the interaction between the magnetic field of the planet and the solar wind). Here, in the case of Saturn, we realized that some of the auroras are not only produced by the surrounding magnetosphere, but also by these famous winds, which swirl in its own atmosphere.
“The turnover rate seemed to change over time”
James O’Donoghue, co-author of the study
The authors see in this characteristic direct evidence that Saturn’s measured variable rotation rate is driven by these fluxes “. In other words: it is these winds that explain why there have been recorded time differences, compared to the real period it takes Saturn to perform a rotation (a turn on itself). The Cassini probe, which arrived in 2004 to the planet, had notably obtained different measurements over time. ” Not only did the rate of rotation seem to change over time, but the north and south poles also seemed to rotate at their own pace. », abstract James O’Donoghue.
Now scientists know why they could only get a rough estimate of Saturn’s day length by studying its magnetic field. It was because of these winds present in the upper polar atmosphere of Saturn.