Giant storm grips Saturn

Eu­ro­pe­an and Amer­i­can as­tro­no­mers have teamed up to study a rare storm on Sat­urn in more de­tail than ev­er be­fore pos­si­ble.
 

The ringed plan­et’s gas­e­ous sur­face nor­mally looks plac­id. But once ev­ery 30 Earth years or so - one Sa­turn year - as spring washes over its north­ern half, some­thing stirs deep be­low the clouds, sci­en­tists say, lead­ing to a great plan­et-wide dis­turb­ance. 

There’s now “a gi­gantic, vi­o­lent and com­plex erup­tion of bright cloud ma­te­ri­al, which has spread to en­cir­cle the en­tire plan­et,” said Leigh Fletch­er of the Un­ivers­ity of Ox­ford, U.K., lead au­thor of a study on the events to ap­pear May 19 in the re­search jour­nal Sci­ence.

An in­stru­ment on NASA’s Cas­si­ni space­craft, or­bit­ing the gi­ant plan­et, first de­tected the storm last De­cem­ber. As­tro­no­mers an­a­lyzed it in fur­ther de­tail with an in­fra­red cam­era on the Eu­ro­pe­an South­ern Ob­ser­va­to­ry’s Very Large Tel­e­scope at Cerro Paranal, Chile. Am­a­teur as­tro­no­mers have al­so joined the hunt. Only the sixth such storm spot­ted since 1876, it’s al­so the first to be ob­served by an or­bit­ing craft and to be stud­ied in the ther­mal in­fra­red light, which re­veals tem­per­a­ture varia­t­ions in the storm. 

Pre­vi­ous stud­ies “have only been able to use re­flected sun­light, but now, by ob­serv­ing ther­mal in­fra­red light for the first time, we can re­veal hid­den re­gions of the at­mos­phere and meas­ure the really sub­stantial changes in tem­per­a­tures and winds,” Fletch­er said.

The storm may have orig­i­nat­ed deep down in the wa­ter clouds where a thunderstorm-like pro­cess trig­gered a huge “con­vec­tive plume,” sci­en­tists say: just as hot air rises above a heat­er, a mass of gas would have head­ed up and punched through Sat­urn’s usu­ally calm up­per at­mos­phere. The huge dis­turb­ances in­ter­act with the cir­cu­lat­ing winds mov­ing east and west and cause wild tem­per­a­ture swings high up in the skies.

“Our new ob­serva­t­ions show that the storm had a ma­jor ef­fect on the at­mos­phere, trans­port­ing en­er­gy and ma­te­ri­al over great dis­tances, mod­i­fy­ing the at­mos­pher­ic winds - cre­at­ing me­an­der­ing je­t streams and form­ing gi­ant vor­ti­ces - and dis­rupt­ing Sat­urn’s slow sea­son­al evo­lu­tion,” adds Glenn Or­ton of the Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na, Calif., an­oth­er of the re­search­ers.

Some un­ex­pected fea­tures seen through the Very Large Tel­e­scope have been dubbed “strato­spheric bea­cons”—warm spots in the strat­o­sphere, 250 to 300 km (155 to 190 miles) above low­er at­mos­phere cloud tops, that show how far up­ward the stor­m’s ef­fects ex­tend. Sat­urn’s strat­o­sphere is nor­mally around mi­nus 130 de­grees Cel­si­us (mi­nus 200 Fahr­en­heit) at this sea­son but the bea­cons are meas­ured to be 15-20 de­grees Cel­si­us warm­er.

That means that though they’re in­vis­i­ble in to the un­aided eye, they can out­shine the rest of the plan­et in the ther­mal in­fra­red light, as­tro­no­mers say. They had nev­er been de­tected be­fore, so re­search­ers aren’t sure how com­mon they are. “We are con­tin­u­ing to ob­serve this once-in-a-genera­t­ion even­t,” Fletch­er said.