美宇航局观测到土星上风暴过后的情形

NASA's Cassini spacecraft has tracked the aftermath of a rare massive storm on Saturn¹. Data reveal record-setting disturbances³ in the planet's upper atmosphere long after the visible signs of the storm abated⁴（减轻）, in addition to an indication the storm was more forceful than scientists previously⁵ thought. Data from Cassini's composite infrared⁶ spectrometer (CIRS) instrument revealed the storm's powerful discharge sent the temperature in Saturn's stratosphere（同温层） soaring 150 degrees Fahrenheit⁷ (83 kelvins) above normal. At the same time, researchers at NASA's Goddard Space Flight Center in Greenbelt, Md., detected a huge increase in the amount of ethylene（乙烯） gas, the origin of which is a mystery. Ethylene, an odorless, colorless gas, isn't typically observed on Saturn. On Earth, it is created by natural and human-made sources.

 

Goddard scientists describe the unprecedented⁸ belch⁹（打嗝，喷出物） of energy in a paper to be published in the Nov. 20 issue of the Astrophysical Journal.

 

"This temperature spike¹⁰ is so extreme it's almost unbelievable, especially in this part of Saturn's atmosphere, which typically is very stable," said Brigette Hesman, the study's lead author and a University of Maryland scientist who works at Goddard. "To get a temperature change of the same scale on Earth, you'd be going from the depths of winter in Fairbanks, Alaska, to the height of summer in the Mojave Desert."

 

First detected by Cassini in Saturn's northern hemisphere on Dec. 5, 2010, the storm grew so large that an equivalent storm on Earth would blanket most of North America from north to south and wrap around our planet many times. This type of giant disturbance² on Saturn typically occurs every 30 Earth years, or once every Saturn year.

 

Not only was this the first storm of its kind to be studied by a spacecraft in orbit around the planet, but it was the first to be observed at thermal¹¹ infrared wavelengths¹². Infrared data from CIRS allowed scientists to take the temperature of Saturn's atmosphere and to track phenomena¹³ that are invisible to the naked eye.

 

Temperature measurements by CIRS, first published in May 2011, revealed two unusual beacons¹⁴ of warmer-than-normal air shining brightly in the stratosphere. These indicated a massive release of energy into the atmosphere. After the visible signs of the storm started to fade, CIRS data revealed the two beacons had merged¹⁵. The temperature of this combined air mass shot up to more than minus 64 degrees Fahrenheit (above 220 kelvins).

 

According to Hesman, the huge spike of ethylene generated at the same time peaked with 100 times more ethylene than scientists thought possible for Saturn. Goddard scientists confirmed the release of the gas using the Celeste spectrometer mounted on the McMath-Pierce Solar Telescope on Kitt Peak in Arizona.

 

The team still is exploring the origin of the ethylene, but has ruled out a large reservoir deep in the atmosphere.

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