Saturn’s “Great White Spot”

Spotting Saturn’s Northern Storm

NASA’s Cassini spacecraft captures a composite near-true-color view of the huge storm churning through the atmosphere in Saturn’s northern hemisphere.

This storm is the largest and most intense observed on Saturn by NASA’s Voyager or Cassini spacecraft. The storm is still active. As scientists have tracked this storm over several months, they have found it covers 500 times the area of the biggest of the southern hemisphere storms observed earlier in the Cassini mission (see PIA06197 and PIA12576). The shadow cast by Saturn’s rings has a strong seasonal effect, and it is possible that the switch to powerful storms now being located in the northern hemisphere is related to the change of seasons after the planet’s August 2009 equinox.

In an image captured Dec. 5, 2010, scientists saw a small white spot with a size of about 800 miles (1,300 kilometers) north-to-south and 1,600 miles (2,500 kilometers) east-to-west. In this view, taken on Dec. 24, 2010, the storm has grown to a north-to-south, or latitudinal, extent of about 6,000 miles (10,000 kilometers) three weeks after the storm started. The main part of the storm has an east-to-west, or longitudinal, extent of about 11,000 miles (17,000 kilometers) in this view. Other images taken at the same time show the tail extending almost one-third of the way around the planet – a distance of 62,000 miles (100,000 kilometers).

See PIA12825 for a false-color view taken about two months after this view, with the storm’s tail encircling the planet and the latitudinal extent swollen to almost 9,000 miles (15,000 kilometers).

Periodic, huge storms called Great White Spots have been observed in previous Saturnian years (each of which is about 30 Earth years), usually appearing in late northern summer. Saturn is now experiencing early northern spring, so this storm, if it is a Great White Spot, is happening earlier than usual. This storm is about as large as the largest of the Great White Spots, which also encircled the planet but had latitudinal sizes ranging up to 12,000 miles (20,000 kilometers). The Voyager and Cassini spacecraft were not at Saturn for previous Great White Spot appearances.

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