A jet stream, shown in this near-infrared image from Cassini as a narrow orange band, cutting across the zones of Saturn’s atmosphere. Reds and oranges indicate clouds deep in the atmosphere, yellows and greens indicate intermediate clouds, and white and blue indicate high clouds and haze. (NASA/JPL-Caltech/SSI)
Saturn has turbulent jet streams – regions where winds blow especially fast – on a much greater scale than those in the Earth’s atmosphere: and that’s not the only difference. Earth’s jet streams get their energy from solar heating, whereas data from NASA’s Cassini spacecraft have now shown that Saturn’s jet streams are powered by heat rising from the planet’s interior.
Saturn has a deep and complex atmosphere with clouds at many levels. As on Earth, condensation and cloud formation play an important role in driving circulation. Cassini has now been orbiting Saturn for long enough to provide useful cloud tracking data at two different altitudes, at both visible and near-infrared wavelengths, in order to track the jet streams. They occur in places where there is a significant temperature variation from latitude to latitude, most directed eastwards, some westwards. Data from 2005–2012 show eddies accelerating the jet streams, as a result of condensation. But the eddies were weak at high levels in Saturn’s troposphere, where solar heating is strong, and stronger at greater depths that matched the tops of the ammonia clouds. As a result, researchers suggest that it is Saturn’s internal heat that drives the jet streams, as water vapour from deep in the atmosphere condenses, releasing heat. It’s the same mechanism as on Earth, but here it is driven by the Sun’s heating, whereas on Saturn solar heating is not significant.
This image is published in the August 2012 issue of Astronomy & Geophysics magazine.