Saturn's spin mystery solved with the Webb telescope
Saturn is not speeding up or slowing down. Its aurora drives winds and currents that create the illusion of a changing rotation, a new study finds.
- Saturn is not changing its true spin rate, earlier data created the illusion
- The aurora heats the atmosphere and drives winds and electric currents in a self-sustaining loop
- Webb measured temperature and particle density about ten times more precisely than past instruments
- The puzzle dates back to readings from the Cassini probe in 2004
A decades-old puzzle about Saturn’s apparently shifting rotation now seems to have an answer. A team led by Professor Tom Stallard of Northumbria University announced on May 29 that the planet is neither speeding up nor slowing down, and that processes high in its atmosphere only make it look that way.
The key lies in the aurora, the polar glow that sets off a chain of physical effects on Saturn. Astronomers have been trying to explain the illusion since the Cassini probe recorded signals back in 2004 that suggested a spin rate which seemed to drift over time.
How does the aurora fool rotation measurements?
Saturn has no solid surface from which a spin rate can be read directly, so scientists rely on radio signals and the magnetic field. The aurora at the poles heats the upper atmosphere and drives strong winds, and those winds in turn generate electric currents.
Those currents shift the very signals used to gauge rotation, so the speed appeared to change even though the planet’s underlying spin stays steady. Stallard described the process as a closed loop that powers itself.
What we are seeing is essentially a planetary heat pump. Saturn’s aurora heats the atmosphere, the atmosphere drives winds, the winds produce currents that feed the aurora, and round it goes.
What did Webb measure differently?
The James Webb telescope observed Saturn through a full planetary day, tracking temperature and particle density in the atmosphere. Those measurements were roughly ten times more precise than what earlier instruments could deliver.
That added precision let the team separate the real spin from the effects created by the aurora. The data revealed an asymmetric temperature pattern at the poles, confirming the link between the heated atmosphere, the winds and the currents.
The work appeared in the Journal of Geophysical Research: Space Physics. The authors stress that the finding explains this specific Saturn puzzle, but they do not claim the same mechanism applies equally to every gas giant, something further observations will need to test.
Could a similar heat cycle also explain odd rotation readings on other planets with strong auroras?
