The upper atmosphere of the gas giants (Saturn, Jupiter, Uranus, and Neptune) is believed to be as hot as that of Earth. But unlike Earth, the Sun is too far from these outer planets to explain such high temperatures. The source of this heat is one of the great mysteries of planetary science.
A new analysis of data from NASA's Cassini spacecraft has finally allowed scientists to come up with a viable theory of what exactly heats the upper layers of Saturn and possibly other gas giants so much. The researchers concluded that these are the auroras at the north and south poles of the planet. These are electrical currents generated by interactions between solar winds and charged particles from Saturn's moons. It is they who form the aurora and heat the upper atmosphere.
The study was published in the journal Nature Astronomy and is by far the most reasoned explanation for both the temperature and density of the gas giant's upper atmosphere – an area that is still poorly understood.
It was measuring the density of the atmosphere that allowed scientists to obtain the information needed to determine temperature. Density decreases with height, and the rate of decline depends on temperature. They found the temperature peaks near the auroras, indicating that polar electric currents are heating the upper atmosphere.
In addition, the measurements of density and temperature combined helped scientists figure out wind speed. Understanding Saturn's upper atmosphere, where the planet meets space, is key to understanding space weather and its effects on other planets in our solar system and exoplanets in the orbits of other stars.
