A massive
whirling vortex recently discovered over Saturn's south pole has features that
are similar to hurricanes on Earth and unlike anything astronomers have seen
before, a new study finds.
The polar
vortex was first discovered by NASA's Cassini
spacecraft on Oct. 11, 2006, as it flew over the gas giant's south pole.
The mass of swirling clouds took scientists by surprise.
"This
is something we have never seen before," said study team leader Ulyana
Dyudina of Caltech. "Before Cassini, we didn't know such a feature could exist
on the poles."
Dyudina and
her colleagues used more than three hours of observations of the vortex to
examine its dynamics and structure. False color images of cloud heights showed
a dark, red central
eye similar to those at the center of terrestrial hurricanes, indicating
that the upper atmosphere in the eye was nearly cloud-free.
Two eye walls
encircle the eye and their clouds rotate in the same direction as the planet
does, just as they do in hurricanes. Eyes and eye walls have never been
observed anywhere else except on Earth.
Saturn's
polar vortex is much bigger than any hurricane found on Earth though: Its eye
alone measures about 2,500 miles (4,000 kilometers) in diameter, Dyudina told SPACE.com.
The eye of a typical terrestrial hurricane is often just 2 or 3 miles wide.
Exactly
what drives the vortex is uncertain, but it's not the warm ocean moisture that
fuels hurricanes on Earth. Dyudina said that it could be supported by the
moisture-driven motion of clouds in the lower atmosphere, but that scientists
have no way to tell just yet.
The vortex
also differs from hurricanes because it is stationary, constantly spinning over
the same portion of the south pole. Polar vortices have been observed on other
planets (they cover the North and South Pole of Earth), but unlike any of these
vortices, Saturn's core
eye is warm. In contrast, the polar vortices of Earth have cold cores.
As Saturn's
year (about 29.5 Earth-years) shifts so that the sun no longer shines on the
south pole and begins to illuminate the north pole, Dyudina hopes that
Cassini's extended mission will allow scientists to observe indications of a
north pole vortex and to continue observing the south pole vortex to see if
they are permanent features and how the vortices fit into the planet's overall
atmospheric circulation.
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