Saturn: officially a cool, hot planet

Scientists will have to go back to the drawing board to find an explanation for the hotter than expected temperatures in the upper atmospheres of the gas giants. New research modelling the upper atmosphere of Saturn has shown that the process put forward to explain the heating actually has a cooling effect.

A broad brush calculation to find the temperature of a planet's upper atmosphere just balances the amount of incident sunlight, with the amount of heat lost to the lower atmosphere. But our solar system's gas giants are consistently hotter than expected.

Theoreticians proposed that the extra heat might be due to the ionosphere, being driven by the planet's magnetic field. This interaction works to heat Earth's atmosphere around the Northern Lights.

But on Saturn, winds driven by energy entering the ionosphere at the poles actually serve to cool the planet's atmosphere, rather than heat it, according to new research published in the 25 January edition of the journal Nature.

One of the study's authors, UCL professor Alan Aylward, says: "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." ®