29 April 2013
Giant vortex at Saturn's north pole finally revealed
by Will Parker
The Cassini spacecraft has provided scientists with the first close-up views of a massive hurricane-like vortex swirling around Saturn's north pole. The vortex - about 20 times larger than the average hurricane on Earth - spins inside a large, mysterious, six-sided weather pattern which astronomers call "the hexagon."
"We did a double take when we saw this vortex because it looks so much like a hurricane on Earth," said Andrew Ingersoll, a Cassini imaging team member. "But there it is at Saturn, on a much larger scale, and it is somehow getting by on the small amounts of water vapor in Saturn's hydrogen atmosphere."
Ingersoll said there were similarities between the Saturn vortex and Earth hurricanes. Both have a central eye with no clouds or very low clouds and both have high clouds forming an eye wall, other high clouds spiraling around the eye, and a counter-clockwise spin in the northern hemisphere.
A major difference between the hurricanes is that the one on Saturn is much bigger than its counterparts on Earth and spins surprisingly fast. On Saturn, the wind in the eye wall blows more than four times faster than hurricane force winds on Earth. Unlike terrestrial hurricanes, which tend to move, the Saturnian hurricane is locked onto the planet's north pole. On Earth, hurricanes tend to drift northward because of the forces acting on the fast swirls of wind as the planet rotates. The one on Saturn does not drift and is already as far north as it can be.
Scientists believe the massive storm has been churning for years. When Cassini arrived in the Saturn system in 2004, Saturn's north pole was dark because the planet was in the middle of its north polar winter. During that time, the Cassini spacecraft's composite infrared spectrometer and visual and infrared mapping spectrometer detected a great vortex, but a visible-light view had to wait for the passing of the equinox in August 2009. Only then did sunlight begin flooding Saturn's northern hemisphere.
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