Cassini spacecraft captures large storm on Saturn

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Friday, July 8, 2011

Saturn showing the Great White Spot.
Image: spacetelescope.org.

On Wednesday NASA released details of a giant convective storm on Saturn gathered from the international Cassini spacecraft orbiting the planet. The storm, known as a "Great White Spot", is around 6,200 miles (10,000 kilometers) wide and visible from Earth.

The White Spot storms have been observed since 1876 and occur approximately every 30 years; only five previous storms have been seen in the last 137 years. The first signs were detected on December 5, 2010 by instruments aboard the Cassini spacecraft when it recorded lightening outbursts in a small bright area on Saturn's northern half. The area was tracked by the spacecraft and by astronomers on the ground through telescopes. It was later identified as a brewing storm during the start of Saturn spring. Its size and intensity grew until its tail wrapped around the planet. It now covers 1.5 billion square miles.

Cassini has been monitoring storms on Saturn since the craft arrived there in 2004. This is the most intense yet seen and was observed in unprecedented detail, according to the journal Nature in two papers published Thursday. The storm is 500 times larger than the biggest storm on Saturn monitored by Cassini. The spacecraft's instruments showed the rate of the nearly continuous lightning flashes was up to ten times more frequent than during past storms it has monitored. This electrical activity is 10,000 times stronger than lightning bursts measured on Earth.

Saturn's huge storm is bright due to its gaseous content, scientists say.

A key question is the source of the energy powering Great White Spots. Originally researchers thought the storms' power might come from the sun. However, researcher Agustin Sánchez-Lavega told Space.com the new data showed that to make sense of the cloud patterns, the winds must "extend deep into the 'weather layer' ... where the main clouds reside." Since sunlight does not reach this depth, this "points to the action of an internal heat source as the power for the winds."


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