"Long before it's in the papers"
January 27, 2015


Measurements show Jupiter’s “Red Spot” shrinking dramatically

May 16, 2014
Courtesy of NASA
and World Science staff

Ju­pi­ter’s trade­mark Great Red Spot—a swirling storm fea­ture larg­er than Earth—has shrunk to its small­est size ev­er meas­ured, as­tro­no­mers re­port.

The rea­sons for the shrink­age is un­known, but it’s ac­cel­er­at­ing, as­tro­no­mers said. If it con­tin­ues at re­cently meas­ured rates, the fa­mous blotch will be gone by about 2030.

Hub­ble Space Tel­e­scope im­ages doc­u­ment­ing the Great Red Spot be­gin­ning in 1995 with a view from the tele­scope's Wide Field and Plan­e­tary Cam­era 2 (WF­PC2) when the long ax­is of the Great Red Spot was es­ti­mat­ed to be 13,020 miles (20,950 kilo­me­ters) across. This cam­era was built by NA­SA's Je­t Pro­pul­sion Lab­o­ra­to­ry in Pas­a­de­na, Cal­i­for­nia, and cor­rected the tele­scope's in­i­tial blur­ry vi­sion. In a 2009 pho­to, af­ter WF­PC2 had been re­placed by the Wide Field Cam­era 3 (WFC3), the storm was meas­ured at 11,130 miles (17,910 kilo­me­ters) across. (Cour­te­sy NA­SA/JPL)

If Earth’s sur­face were spread out like an or­ange peel, about one and a half of those would fit with­in the Red Spot to­day. But in 1979, that num­ber was over three­—and back in Vic­to­ri­an days, it was es­ti­mat­ed around 10.

Re­cent NASA Hub­ble Space Tel­e­scope ob­serva­t­ions show the plan­et­ary pim­ple is about 10,250 miles (16,500 km) wide, said Amy Si­mon of NASA’s God­dard Space Flight Cen­ter in Green­belt, Md.

Ob­serva­t­ions as far back as the late 1800s gauged the Red Spot to be as big as 25,500 miles (41,000 km) on its long end. And NASA’s Voy­ag­er 1 and Voy­ag­er 2 fly­bys of Ju­pi­ter in 1979 meas­ured the storm as 14,500 miles (23,300 km) across.

Be­gin­ning in 2012, am­a­teur ob­serva­t­ions re­vealed a no­tice­a­ble ac­celera­t­ion in the shrink­age—to 580 miles (930 km) per year—chang­ing its shape from an oval to a cir­cle, as­tro­no­mers said.

“It is ap­par­ent that very small ed­dies are feed­ing in­to the stor­m” on the gas-gi­ant plan­et, said Si­mon. “These may be re­spon­si­ble for the ac­cel­er­ated change” by alter­ing the storm’s in­ter­nal dy­nam­ics and en­er­gy. Her team plans to study the ed­dies’ mo­tions and the in­ter­nal storm dy­nam­ics to de­ter­mine wheth­er the ed­dies can feed or sap mo­men­tum en­ter­ing the up­welling vor­tex, caus­ing the shrink­age.

* * *

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Jupiter’s trademark Great Red Spot—a swirling storm feature larger than Earth—has shrunk to its smallest size ever measured, astronomers report. The reasons for the shrinkage is unknown, but it’s accelerating, astronomers said. If it continues at recently measured rates, the famous blotch will be gone by about 2030. If Earth’s surface were spread out like an orange peel, about one and a half of those would fit within the Red Spot today. But in 1979, that number was over three—and back in Victorian days, it was estimated around 10. According to Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, recent NASA Hubble Space Telescope observations show the Red Spot is about 10,250 miles (16,500 kilometers) wide. Observations as far back as the late 1800s gauged the Red Spot to be as big as 25,500 miles (41,000 kilometers) on its long end. And NASA’s Voyager 1 and Voyager 2 flybys of Jupiter in 1979 measured the storm as 14,500 miles (23,300 kilometers) across. In recent comparison images, one Hubble photo was taken in 1995 by the Hubble’s Wide Field and Planetary Camera 2 when the spot’s long axis was estimated to be 13,020 miles (20,950 kilometers) across. In 2009, after that camera had been replaced by the Wide Field Camera 3, the storm was measured at 11,130 miles (17,910 kilometers). Beginning in 2012, amateur observations revealed a noticeable acceleration in the shrinkage—to 580 miles (930 kilometers) per year—changing its shape from an oval to a circle, astronomers said. “It is apparent that very small eddies are feeding into the storm,” said Simon. “These may be responsible for the accelerated change” by changing its internal dynamics and energy. Her team plans to study the eddies’ motions and the internal storm dynamics to determine whether the eddies can feed or sap momentum entering the upwelling vortex, causing the shrinkage.