In the hunt for interplanetary answers to how atmospheric temperatures are maintained, UCL researchers have ruled out a long held theory. They’ve found that the hotter than expected temperature of Saturn’s upper atmosphere — and that of the other giant planets — isn’t due to the same mechanism that heats the atmosphere around the Earth’s Northern Lights.

A simple calculation to give the expected temperature of a planet’s upper atmosphere balances the amount of sunlight absorbed by the energy lost to the lower atmosphere. But the calculated values don’t tally with the actual observations of the Gas Giants: they are consistently much hotter.

It has long been thought that motion within the electrically charged part of the atmosphere, the ionosphere, is driven by the planet’s magnetic field, or magnetosphere, was the culprit behind this heating process. Now writing in the journal Nature, the researchers reveal, using numerical models of Saturn’s atmosphere, that the net effects of the winds driven by polar energy inputs is not to heat the atmosphere but actually cools it.

Professor Alan Aylward, of the UCL Department of Physics & Astronomy, and an author of the study, explains: “The aurora has been studied for over a hundred years, yet our discovery takes us back to first principles. We need to re-examine our basic assumptions about planetary atmospheres and what causes the observed heating.”

“Studying what happens on planets such as Saturn gives us an insight into what happens closer to home. 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.”

The study was funded by the UK Particle Physics and Astronomy Research Council (PPARC) and Sun Microsystems Ltd.

Notes to editors

The paper ‘An unexpected cooling effect in Saturn’s upper atmosphere’ is published in the January 25th edition of the journal Nature. C. G. A. Smith

[1], A. D. Aylward [1], G. H. Millward [1{, S. Miller [1] & L. E. Moore [2]

[1] Department of Physics and Astronomy, University College London, WC1E

[2] Center for Space Physics, Boston University, Boston, Massachusetts

02215, USA. {Present address: Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA.