NASA's Cassini spacecraft has obtained the
highest-resolution movie yet of a unique six-sided jet
stream, known as the hexagon, around Saturn's north pole.
This is the first hexagon movie of its
kind, using color filters, and the first
to show a complete view of the top of
Saturn down to about 70 degrees
latitude. Spanning about 20,000 miles
(30,000 kilometers) across, the
hexagon is a wavy jet stream of 200-
mile-per-hour winds (about 322
kilometers per hour) with a massive,
rotating storm at the center. There is
no weather feature exactly,
consistently like this anywhere else
in the solar system.
"The hexagon is just a current of air, and weather features
out there that share similarities to this are notoriously
turbulent and unstable," said Andrew Ingersoll, a Cassini
imaging team member at the California Institute of
Technology in Pasadena. "A hurricane on Earth typically
lasts a week, but this has been here for decades -- and who
knows -- maybe centuries."
Weather patterns on Earth are interrupted when they
encounter friction from landforms or ice caps. Scientists
suspect the stability of the hexagon has something to do
with the lack of solid landforms on Saturn, which is
essentially a giant ball of gas.
Better views of the hexagon are available now because the
sun began to illuminate its interior in late 2012. Cassini
captured images of the hexagon over a 10-hour time span
with high-resolution cameras, giving scientists a good look
at the motion of cloud structures within.
They saw the storm around the pole, as well as small
vortices rotating in the opposite direction of the hexagon.
Some of the vortices are swept along with the jet stream as
if on a racetrack. The largest of these vortices spans about
2,200 miles (3,500 kilometers), or about twice the size of the
largest hurricane recorded on Earth.
Scientists analyzed these images in false color, a rendering
method that makes it easier to distinguish differences
among the types of particles suspended in the atmosphere
-- relatively small particles that make up haze -- inside and
outside the hexagon.
"Inside the hexagon, there are fewer large haze particles and
a concentration of small haze particles, while outside the
hexagon, the opposite is true," said Kunio Sayanagi, a
Cassini imaging team associate at Hampton University in
Virginia. "The hexagonal jet stream is acting like a barrier,
which results in something like Earth's Antarctic ozone
hole."
The Antarctic ozone hole forms within a region enclosed by
a jet stream with similarities to the hexagon. Wintertime
conditions enable ozone-destroying chemical processes to
occur, and the jet stream prevents a resupply of ozone from
the outside. At Saturn, large aerosols cannot cross into the
hexagonal jet stream from outside, and large aerosol
particles are created when sunlight shines on the
atmosphere. Only recently, with the start of Saturn's
northern spring in August 2009, did sunlight begin bathing
the planet's northern hemisphere.
"As we approach Saturn's summer solstice in 2017, lighting
conditions over its north pole will improve, and we are
excited to track the changes that occur both inside and
outside the hexagon boundary," said Scott Edgington,
Cassini deputy project scientist at NASA's Jet Propulsion
Laboratory in Pasadena, Calif.
A black-and-white version of the imaging camera movie and
movies obtained by Cassini's visual and infrared mapping
spectrometer are also tools Cassini scientists can use to
look at wind speeds and the mini-storms inside the jet
stream.
Cassini launched in 1997 and arrived at Saturn on July 1,
2004. Its mission is scheduled to end in September 2017.
The Cassini-Huygens mission is a cooperative project of
NASA, the European Space Agency and the Italian Space
Agency. JPL manages the mission for NASA's Science
Mission Directorate in Washington. JPL designed, developed
and assembled the Cassini orbiter and its two onboard
cameras. The imaging team is based at the Space Science
Institute, Boulder, Colo.
No comments:
Post a Comment