NASA's Cassini Spacecraft Solves Mystery of Saturn's Jet Streams

By Chelsea Whyte on June 26, 2012 11:36 PM EDT

saturn's jet streams
A particularly strong jet stream churns through Saturn's northern hemisphere in this false-color view from NASA's Cassini spacecraft. (Photo: NASA/JPL-Caltech/SSI)

The years-long search for the cause of the turbulent jet streams that churn east to west across Saturn's face has come to an end.

Temperature differences in the atmosphere that cause eddies to swirl and feed the jet streams - regions where winds blow faster than other places - don't come from the sun acting on Saturn. That's how it works on Earth, but on the solar system's largest globe, internal heating caused by condensation in Saturn's atmosphere is driving the rotating air systems, which turn like gears that move a conveyer belt of wind around the planet.

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"We know the atmospheres of planets such as Saturn and Jupiter can get their energy from only two places: the sun or the internal heating. The challenge has been coming up with ways to use the data so that we can tell the difference," said Tony Del Genio of NASA's Goddard Institute for Space Studies, the lead author of the paper and a member of the team that manages NASA's Cassini spacecraft.

Cassini has been in orbit around Saturn long enough to gather the large number of observations the team needed to differentiate the subtle patterns from the day-to-day variations in weather.

"Understanding what drives the meteorology on Saturn, and in general on gaseous planets, has been one of our cardinal goals since the inception of the Cassini mission," said Carolyn Porco, imaging team lead, based at the Space Science Institute. "It is very gratifying to see that we're finally coming to understand those atmospheric processes that make Earth similar to, and also different from, other planets."

There are profound differences between the atmospheres of Earth and Saturn, reports EarthSky.org. For one, Saturn is about 10 times farther from the sun than Earth. Plus Earth's atmosphere is relatively thin, and lies atop a solid-and-liquid surface. In contrast, Saturn is a gas giant world, with nothing we can meaningfully call a surface.

A series of jet streams cut across Saturn, some visible to the naked eye, and they crop up when there is a significant difference in temperature from one layer to another. Some of the streams that are lower in the atmosphere are only visible through near-infrared light, and the filters on Cassini's cameras allowed scientists to see into the lower layers.

One filtered view shows the upper part of the troposphere, a high layer of the atmosphere where Cassini sees thick, high-altitude hazes and where heating by the sun is strong. Views through another filter capture images deeper down, at the tops of ammonia ice clouds, where solar heating is weak but closer to where weather originates. This is where water condenses and makes clouds and rain.   

In the new study, which is a follow-up to results published in 2007, the authors used automated cloud tracking software to analyze the movements and speeds of clouds seen in hundreds of Cassini images from 2005 through 2012.

"With our improved tracking algorithm, we've been able to extract nearly 120,000 wind vectors from 560 images, giving us an unprecedented picture of Saturn's wind flow at two independent altitudes on a global scale," said co-author John Barbara, also at the Goddard Institute for Space Studies.

The scientists think that internal heat from Saturn is stirring up water vapor from the planet's interior. This water vapor condenses in places as air rises, releasing heat as clouds and rain are produced. It is this heat that ultimately drives the jet streams, according to Mother Nature Network. Such condensation heating is also the chief driver of storms on Saturn, researchers said.

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