For years, Saturn seemed to be doing something unattainable.
Measurements suggested the enormous planet’s rotation rate was changing over time, as if Saturn were in some way speeding up or slowing down. That puzzling result left scientists trying to find answers. Now, researchers using the James Webb Space Telescope (JWST) say they’ve finally solved the mystery.
The brand new findings, published within the Journal of Geophysical Research: Space Physics, reveal that Saturn’s spectacular northern lights are at the center of the phenomenon. The study shows that the planet’s aurora drives a robust cycle involving heat, winds, and electrical currents that could make Saturn appear to spin at different speeds depending on the way it is measured.
Saturn’s Rotation Mystery
The puzzle dates back many years, however it gained renewed attention after observations from NASA’s Cassini spacecraft in 2004 suggested that Saturn’s rotation rate was step by step changing.
That result was difficult to elucidate because planets don’t simply alter their spin rates on short timescales.
In 2021, a team led by Professor Tom Stallard of Northumbria University proposed a unique explanation. Their research showed that Saturn’s rotation was not actually changing. As a substitute, electrical signals linked to the planet’s aurora were being affected by winds in Saturn’s upper atmosphere. Those winds generated electrical currents that altered the auroral signal scientists were using to estimate the planet’s rotation.
While that study explained the misleading measurements, one major query remained unanswered: What was driving those atmospheric winds?
James Webb Maps Saturn’s Aurora
To research, Stallard and colleagues from institutions across the UK and United States turned to the James Webb Space Telescope.
The team observed Saturn’s northern auroral region repeatedly for a whole Saturnian day. The observations provided a level of detail that previous instruments couldn’t achieve.
Researchers focused on infrared light emitted by a molecule generally known as trihydrogen cation. This molecule forms in Saturn’s upper atmosphere and serves as a natural indicator of temperature. By analyzing its glow, the team created essentially the most detailed maps ever produced of temperatures and charged particle densities inside Saturn’s auroral region.
The advance in accuracy was dramatic. Earlier measurements carried uncertainties of roughly 50 degrees Celsius, making it difficult to detect subtle changes. JWST’s observations were about ten times more precise, allowing scientists to discover localized patterns of heating and cooling for the primary time.
A Self-Sustaining Planetary Heat Engine
The brand new data closely matched predictions from computer models developed greater than a decade ago. Nevertheless, the models only worked if the source of the atmospheric heating was situated exactly where the strongest auroral particles enter Saturn’s atmosphere.
The outcomes indicate that Saturn’s aurora is doing way over creating a blinding light show.
Energy deposited by the aurora heats specific regions of the atmosphere. That heating generates winds, which then create electrical currents. Those currents help power the aurora itself, which continues heating the atmosphere and sustaining the complete cycle.
Lead researcher Professor Tom Stallard said: “What we’re seeing is basically a planetary heat pump. Saturn’s aurora heats its atmosphere, the atmosphere drives winds, the winds produce currents that power the aurora, and so it goes on. The system feeds itself.
“For many years, we knew something strange was happening with Saturn’s apparent rotation rate, but we couldn’t explain it. We then showed it was being driven by atmospheric winds, but we still didn’t know why those winds existed. These latest observations, made possible by JWST, finally give us the evidence we would have liked to shut that loop.”
Implications Beyond Saturn
The invention can have significance far beyond a single planet.
Researchers found evidence that Saturn’s atmosphere and magnetosphere are closely connected. The magnetosphere is the vast region of space shaped by the planet’s magnetic field. Activity within the atmosphere appears to influence conditions within the magnetosphere, while the magnetosphere feeds energy back into the atmosphere.
This ongoing exchange could help explain why the method stays stable over long periods.
In response to the researchers, similar interactions may occur on other planets as well.
Professor Stallard added: “This result changes how we take into consideration planetary atmospheres more generally. If a planet’s atmospheric conditions can drive currents out into the encircling space environment, then understanding what is going on within the stratospheres of other worlds may reveal interactions we have now not yet even imagined.”
An International Research Effort
The James Webb Space Telescope is the world’s premier space science observatory. The telescope is designed to review objects throughout the solar system, investigate planets orbiting distant stars, and explore the origins and evolution of the universe. Webb is a global project led by NASA in partnership with ESA (European Space Agency) and CSA (Canadian Space Agency).
The study was conducted by researchers from Northumbria University along with collaborators from Boston University, the University of Leicester, Aberystwyth University, the University of Reading, Imperial College London, Lancaster University, and Johns Hopkins University Applied Physics Laboratory. Funding for the research was provided by the Science and Technology Facilities Council (STFC).