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Stunning new view of Saturn storm shows eye about the size of India

April 29, 2013
Courtesy of NASA 
and World Science staff

NASA’s Cas­si­ni space­craft has pro­vid­ed the first close-up, visi­ble-light views of a gi­gan­tic hur­ri­cane swirl­ing around Sat­urn’s north pole.

In pic­tures and vid­eo (see narrated video here), sci­en­tists see the hur­ri­cane’s eye is about 1,250 miles (2,000 km) wide. That’s 20 times more than the av­er­age hur­ri­cane eye on Earth and would mean the Sat­urn eye co­vers about as much ar­ea as In­dia, Earth’s sev­enth larg­est coun­try. 

The storm in natural colors. Larger image here. ( Credit: NA­SA/JPL-Cal­tech/SSI)


The eye of a hur­ri­cane is a roughly cir­cu­lar ar­ea of light­er winds at the cen­ter. At the out­er edge of the ringed plan­et’s storm, on the oth­er hand, sci­en­tists de­tect thin, bright clouds trav­el­ing 330 miles (530 km) per hour. The hur­ri­cane swirls in­side a larger, mys­te­ri­ous, six-sided weath­er pat­tern known as 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 at the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy in Pas­a­de­na. “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.”

Scientists are rather puzzled as to how the hurri­cane got there with no ocean be­neath, he explained.

Researchers plan to study the hur­ri­cane to gain in­sight in­to Earth hur­ri­canes, which feed off warm ocean wa­ter. Al­though there is no body of wa­ter near these clouds high in Sat­urn’s at­mos­phere, sci­en­tists say learn­ing how these Sat­urnian storms use wa­ter va­por could re­veal more about how Earth hur­ri­canes de­vel­op.

The storm as imaged with filters sensitive to infrared light. Larger image here. (Credit: NA­SA/JPL-Cal­tech/SSI)


Both Earth hur­ri­canes and Sat­urn’s “north po­lar vor­tex,” as it’s called, have cen­tral eyes with no clouds or very low clouds. Oth­er si­m­i­lar fea­tures in­clude 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, though, is that the storm on Sat­urn is much big­ger than its coun­ter­parts on Earth and spins sur­pris­ingly fast, re­search­ers note. At Sat­urn, the wind in the eye wall blows more than four times faster than hur­ri­cane-force winds on Earth. Anoth­er dif­fer­ence: Earth hur­ri­canes tend to drift north­ward be­cause of the forc­es act­ing on the fast swirls of wind as the plan­et ro­tates. The Sat­urn storm does­n’t drift and is al­ready as far north as it can be.

It “has no­where else to go, and that’s likely why it’s stuck at the pole,” said Ku­nio Sayanagi, a Cas­si­ni im­ag­ing team as­so­ci­ate at Hamp­ton Uni­vers­ity in Hamp­ton, Va.

Sci­en­tists be­lieve the mas­sive storm has been churn­ing for years. When Cas­si­ni reached the Sat­urn sys­tem in 2004, the huge gas­e­ous world was deep in its north po­lar win­ter, and pitch black en­vel­oped that pole. 

The reddish area shows the eye of the Saturn storm as imaged with infrared filters. The "fluffy clouds" in the mid­dle are about the size of Texas, says An­drew In­ger­soll, a Cas­si­ni im­ag­ing team mem­ber. Larger image here. ( Credit: NA­SA/JPL-Cal­tech/SSI)


The space­craft de­tected a great vor­tex in in­fra­red light, but a visible-light view had to await the Au­gust 2009 equi­nox, when Sat­urn’s day and night were the same length, and af­ter which sun­light flood­ed the north. See­ing the pole also re­quired re­routing Cas­si­ni’s or­bit.

Such course changes are highly com­pli­cat­ed: they de­pend on fly­bys of Sat­urn’s moon Ti­tan for a gravita­t­ional nudge, as well as care­ful plan­ning years in ad­vance and pre­cisely planned itin­er­ar­ies to en­sure enough pro­pel­lant re­mains to meet fu­ture goals.

“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,” said Scott Edg­ing­ton, Cas­si­ni dep­u­ty proj­ect sci­ent­ist at NASA’s Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na, Ca­lif. 

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NASA’s Cassini spacecraft has provided the first close-up, visible-light views of a gigantic hurricane swirling around Saturn’s north pole. In pictures and video, scientists see the hurricane’s eye is about 1,250 miles (2,000 km) wide. That’s 20 times more than the average hurricane eye on Earth and would mean the Saturn eye covers about as much area as India, Earth’s seventh largest country. The “eye” is a roughly circular area of lighter winds at the center of a hurricane. At the outer edge of the ringed planet’s storm, on the other hand, scientists detect thin, bright clouds traveling 330 miles (530 km) per hour. The hurricane swirls inside a large, mysterious, six-sided weather pattern known as 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 at the California Institute of Technology in Pasadena. “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.” Scientists will study the hurricane to gain insight into Earth hurricanes, which feed off warm ocean water. Although there is no body of water near these clouds high in Saturn’s atmosphere, scientists say learning how these Saturnian storms use water vapor could reveal more about how Earth hurricanes develop. Both a terrestrial hurricane and Saturn’s north polar vortex have a central eye with no clouds or very low clouds. Other similar features include 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, researchers note. At Saturn, the wind in the eye wall blows more than four times faster than hurricane-force winds on Earth. Another difference: Earth hurricanes tend to drift northward because of the forces acting on the fast swirls of wind as the planet rotates. The Saturn storm doesn’t drift and is already as far north as it can be. It “has nowhere else to go, and that’s likely why it’s stuck at the pole,” said Kunio Sayanagi, a Cassini imaging team associate at Hampton University in Hampton, Va. Scientists believe the massive storm has been churning for years. When Cassini reached the Saturn system in 2004, the huge gaseous world was deep in its north polar winter, and pitch black enveloped that pole. The spacecraft detected a great vortex in infrared light, but a visible-light view had to await the August 2009 equinox, when Saturn’s day and night were the same length, and after which sunlight flooded the north. Seeing the pole required changing the angle of Cassini’s orbits. “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,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. These course changes are extremely complicated: they depend on flybys of Saturn’s moon Titan for a gravitational nudge, as well as careful planning years in advance and precisely itineraries to ensure enough propellant remains to meet future goals.