The James Webb Space Telescope (JWST) has resolved a decades-long mystery regarding Saturn's apparent changing rotation rate. Scientists determined that powerful winds in Saturn's upper atmosphere, not a change in the planet's spin, caused the fluctuating measurements. The planet's northern lights actively heat the atmosphere, generating these winds. These winds then create electrical currents, which power the aurora in a self-sustaining cycle.
Previous observations from the National Aeronautics and Space Administration's (NASA) Cassini spacecraft in 2004 suggested Saturn's rotation rate was changing. This was puzzling because planets do not typically alter their spin rates on short timescales. In 2021, a research team proposed that electrical signals linked to Saturn's aurora were affected by atmospheric winds. These winds altered the auroral signal used to estimate the planet's rotation.
Using the JWST, researchers observed Saturn's northern auroral region for an entire Saturnian day. They focused on infrared light from trihydrogen cation, a molecule in Saturn's upper atmosphere that indicates temperature. This allowed for detailed maps of temperatures and charged particle densities in the auroral region. The JWST's observations were ten times more precise than previous measurements.
The new data aligned with computer models developed over a decade ago. These models required the atmospheric heating source to be located where the strongest auroral particles enter Saturn's atmosphere. The aurora's energy heats specific atmospheric regions. This heating generates winds, which create electrical currents. These currents then help power the aurora, continuing the cycle.
This discovery suggests a close connection between Saturn's atmosphere and magnetosphere. The magnetosphere is the region of space shaped by the planet's magnetic field. Atmospheric activity appears to influence the magnetosphere, which in turn feeds energy back into the atmosphere. This exchange may explain the process's long-term stability. Similar interactions could occur on other planets.
The study was published in the *Journal of Geophysical Research: Space Physics*. Researchers from Northumbria University led the effort. Collaborators included institutions from the United Kingdom and the United States. The Science and Technology Facilities Council (STFC) provided funding.
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