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article imageCassini spacecraft's startling images of massive Saturn hurricane

By Robert Myles     May 1, 2013 in Science
NASA has released some of the most breathtaking images yet from the Cassini-Huygens Saturn orbiter, showing a gigantic hurricane gyrating around Saturn’s north pole.
This monster of a storm, estimated at 20 times the size of an average Earth hurricane, has an eye 2000 kilometers (1250 miles) wide. NASA scientists estimate wind speeds at the outer edge, observed from the movement of Saturnian clouds, to be around 330 miles per hour.
According to BBC News, scientists are unsure how long this cyclone has been in progress around Saturn’s north pole. Saturn has a very long winter due to its 29 year long solar orbit. When Cassini arrived in orbit round the ringed planet in 2004, the pole was in darkness. A sunlit north pole of Saturn has not been seen by astronomers in close detail since the Voyager 2 fly-by in 1981.
When Saturn’s north pole was in darkness, Cassini’s composite infrared spectrometer and visual and infrared mapping spectrometer detected a great vortex. Observing the vortex in the visible light spectrum, the huge hurricane now revealed, had to await the passing of the equinox in August 2009. At that stage, Saturn’s northern hemisphere came into sunlight. The spectacular views now released also involved changing in the angle of Cassini's orbits around Saturn to allow Cassini’s cameras to observe the polar regions.
As Scott Edgington, Cassini deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena explained, “Such a stunning and mesmerizing view of the hurricane-like storm at the north pole is only possible because Cassini is on a sportier course, with orbits tilted to loop the spacecraft above and below Saturn's equatorial plane. You cannot see the polar regions very well from an equatorial orbit. Observing the planet from different vantage points reveals more about the cloud layers that cover the entirety of the planet."
Different from hurricanes on Earth
By studying how the massive hurricane on Saturn behaves, observers hope to gain a better understanding of hurricanes on Earth. Hurricanes on Earth build up over the warm waters of Earth’s oceans but on Saturn, there are no such oceans to explain the hurricane-like movement of this storm high in Saturn’s atmosphere. Instead, scientists hope to establish how Saturn’s storms use atmospheric water vapour, a very small part of the gaseous composition of Saturn’s atmosphere, to generate and then sustain their momentum.
A false-color image from NASA s Cassini mission highlights the storms at Saturn s north pole. The ey...
A false-color image from NASA's Cassini mission highlights the storms at Saturn's north pole. The eye of a hurricane-like storm appears dark red while the fast-moving hexagonal jet stream framing it is a yellowish green.
NASA/JPL-Caltech/SSI
Commenting on the images, Andrew Ingersoll, a Cassini imaging team member at California Institute of Technology in Pasadena, said, "We did a double take when we saw this vortex because it looks so much like a hurricane on Earth. But there it is at Saturn, on a much larger scale, and it is somehow getting by on the small amounts of water vapour in Saturn's hydrogen atmosphere."
NASA summarises a number of similarities between hurricanes on Saturn and their terrestrial equivalents:
• Both have a central eye within which are either no clouds or clouds at very low altitude
• High clouds in the storm system form an eye wall
• High altitude clouds spiral around the eye of the storm
• In the northern hemisphere, the storm spins anti-clockwise
But there are a number of major differences between hurricanes on Earth and those of Saturn. The most obvious are the far greater size and speed of Saturnian storms. Winds forming the eye wall of the storm on Saturn bluster along at four times the speed of Earth’s hurricane-force winds.
Another difference is the almost fixed position of the storm on Saturn. Hurricanes on Earth tend to drift northwards as the forces of the Earth’s 24 hour rotation act on such weather systems. On Saturn, the storm system seems to be locked around the planet’s north pole. It doesn’t drift and is already as far north as it can be.
The images of the hurricane on Saturn are just the latest spectacular from Cassini, a mission that has never failed to impress in its 16 years of operations to date. Just recently, Cassini returned some of the most detailed images of Saturn’s moon Titan ever seen, just one of its many visual triumphs.
Cassini’s mission is open-ended with a number of options for mission termination from 2017 onwards ranging from impact into Saturn to taking in the outer gas giants Uranus and Neptune. Until then, careful planning is required for each of Cassini’s changes in orbital inclination every few years. Each projected change in trajectory requires detailed planning years in advance to ensure enough propellant is available for Cassini to maintain operations for future planned orbits and possible further close encounters.
The Cassini-Huygens mission is a joint project of NASA, the European Space Agency and the Italian Space Agency. California Institute of Technology’s Jet Propulsion Laboratory (JPL) in Pasadena manages the mission on behalf of NASA and it was at JPL where the Cassini orbiter and its two onboard cameras were designed, developed and assembled.
More about Cassini mission, cassini orbiter, Saturn, saturn atmosphere, saturn hurricane
 
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