An artist's impression of Saturn's auroras as viewed from the nightside of the planet.
Credit: John Clarke, Denis Grodent, ESA, and NASA
For years astronomers have known that the upper atmospheres of Saturn and other giant planets are hotter than can be explained by absorbed sunlight. Today the mystery deepened.
The phenomenon has long been blamed on a mechanism similar to what creates the aurora, or Northern Lights on Earth. On Earth, magnetic energy in the magnetosphere drives the aurora and heats the upper atmosphere.
But a new calculation reported in today's issue of the journal Nature finds that this mechanism, if at work on Saturn, would actually cool the upper atmosphere at the lower latitudes (closer to the equator). Scientists will have to go back to the drawing board to figure out what's really heating things up.
"This unexplained 'energy crisis' represents a major gap in our understanding of these planets' atmospheres," the scientists write.
"We need to re-examine our basic assumptions about planetary atmospheres and what causes the observed heating," said study team member Alan Aylward of the University College London.
Some as-yet-unknown direct heating mechanism is possibly at work, the scientists speculate. One possibility: the breaking of "buoyancy waves" generated in the lower atmosphere.
Figuring it all out could help researchers model the future of Earth's atmosphere.
"Studying what happens on planets such as Saturn gives us an insight into what happens closer to home," Aylward said. "Planets can lose their atmospheres as we see with Mars. Do we completely understand how this happens? Are there mechanisms heating the gas and causing it to escape that we do not yet fully understand? By studying what happens in other atmospheres we may find clues to Earth's future."