A new study conducted by researchers from the University of Exeter and the Ecole Normale Supérieure de Lyon, France, has revealed how Saturn, the sixth planet from the Sun and the second largest planet in the Solar System, keeps itself looking young and hot.
Cassini spacecraft has recently provided scientists the first close-up, visible-light views of a behemoth hurricane swirling around Saturn’s north pole. The hurricane’s eye is about 1,250 miles (2,000 kilometers) wide, 20 times larger than the average hurricane eye on Earth (NASA / JPL-Caltech / SSI)
As planets age they become darker and cooler. Saturn however is much brighter than expected for a planet of its age – a question that has puzzled scientists since the late 1960s.
In the new study, the scientists have found that layers of gas, generated by physical instability deep within the planet, prevent heat from escaping and have resulted in Saturn failing to cool down at the expected rate.
“Scientists have been wondering for years if Saturn was using an additional source of energy to look so bright but instead our calculations show that Saturn appears young because it can’t cool down,” said Prof Gilles Chabrier, senior author of the study published in the journal Nature Geoscience (arXiv.org version).
“Instead of heat being transported throughout the planet by large scale motions, as previously thought, it must be partly transferred by diffusion across different layers of gas inside Saturn. These separate layers effectively insulate the planet and prevent heat from radiating out efficiently. This keeps Saturn warm and bright.”
Characterized by its distinctive rings, Saturn is one of the largest planets in our Solar System, second only in size to massive Jupiter. It is primarily made of hydrogen and helium and its excessive brightness has previously been attributed to helium rains, the result of helium failing to mix with Saturn’s hydrogen rich atmosphere.
Layered convection, like that recently discovered in Saturn, has been observed in the Earth’s oceans where warm, salty water lies beneath cool and less salty water. The denser, salty water prevents vertical currents forming between the different layers and so heat cannot be transported efficiently upwards.
The findings suggest that the interior structure, composition and thermal evolution of giant planets in our Solar System, and beyond, may be much more complex than previously thought.
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Bibliographic information: Jérémy Leconte & Gilles Chabrier. 2013. Layered convection as the origin of Saturn’s luminosity anomaly. Nature Geoscience 6, 347–350; doi: 10.1038/ngeo1791
