NASA’s Cassini spacecraft has tracked the aftermath of a rare massive storm on Saturn. Data reveal record-setting disturbances in the planet’s upper atmosphere long after the visible signs of the storm abated, in addition to an indication the storm was more forceful than scientists previously thought.


This false-color mosaic from NASA’s Cassini spacecraft shows the tail of Saturn’s huge northern storm. See PIA14905 to learn more about this storm and watch its development over several months. Earlier in the Cassini mission, the spacecraft chronicled a smaller storm in the southern hemisphere called the “Dragon Storm.” See PIA06197 to learn more about that storm and to see a similar, false-color view. The head of the storm is beyond the horizon in this view. Saturn’s atmosphere and its rings are shown here in a false color composite made from 12 images taken in near- infrared light through filters that are sensitive to varying degrees of methane absorption. Red and orange colors in this view indicate clouds that are deep in the atmosphere. Yellow and green colors, most noticeable near the top of the view, indicate intermediate clouds. White and blue indicate high clouds and haze. The rings appear as a thin horizontal line of bright blue because they are outside of the atmosphere and not affected by methane absorption. The oval in the upper left of this image that appears slightly blue is the same hole in the deep clouds of the planet’s atmosphere that can be seen near the tail in a larger false-color mosaic, PIA14903. The blue color comes from the high haze overlying the hole. This view looks toward the northern, sunlit side of the rings from just above the ring plane. The shadow of the moon Enceladus is visible on the planet in the lower left of the image. The images were taken with the Cassini spacecraft wide-angle camera using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 890 nanometers are projected as blue. The images filtered at 728 nanometers are projected as green, and images filtered at 752 nanometers are projected as red. The images were taken on Jan. 12, 2011, over about one hour at a distance of approximately 684,000 miles (1.1 million kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 52 degrees. The images were re-projected to the same viewing geometry, so that scale in this final mosaic is 76 miles (122 kilometers) per pixel. Image credit:NASA/JPL-Caltech/Space Science Institute

Data from Cassini’s composite infrared spectrometer (CIRS) instrument revealed the storm’s powerful discharge sent the temperature in Saturn’s stratosphere soaring 150 degrees Fahrenheit (83 kelvins) above normal. At the same time, researchers at NASA’s Goddard Spaceflight Center in Greenbelt, Md., detected a huge increase in the amount of ethylene 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 man-made sources.

Goddard scientists describe the unprecedented belch of energy in a paper to be published in the Nov. 20 issue of the Astrophysical Journal.

“This temperature spike 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 disturbance 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 thermal infrared wavelengths. Infrared data from CIRS allowed scientists to take the temperature of Saturn’s atmosphere and to track phenomena that are invisible to the naked eye.


This animation shows ‘beacons’ of hot air seen in the infrared that appeared during a great springtime storm on Saturn from January 2011 to March 2012.

Temperature measurements by the composite infrared spectrometer, first published in May 2011, revealed two unusual beacons 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, the instrument’s data revealed the two beacons had merged. 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 of the gas than scientists thought possible for Saturn. Goddard scientists confirmed the release of ethylene 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.

“We’ve really never been able to see ethylene on Saturn before, so this was a complete surprise,” said Goddard’s Michael Flasar, the CIRS team lead.

A complementary paper led by Cassini team associate Leigh Fletcher of Oxford University, England, describes how the two stratospheric beacons merged to become the largest and hottest stratospheric vortex ever detected in our solar system. Initially, it was larger than Jupiter’s Great Red Spot.

Their paper in the journal Icarus, which combines CIRS data with additional infrared images from other Earth-based telescopes, including NASA’s Infrared Telescope Facility at Mauna Kea, Hawaii, also reports a powerful collar of clockwise winds — encompassing a bizarre soup of gases — around the vortex.

“These studies will give us new insight into some of the photochemical processes at work in the stratospheres of Saturn, other giants in our solar system, and beyond,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency, and the Italian Space Agency. The mission is managed by JPL for NASA’s Science Mission Directorate in Washington. Hesman’s work was funded in part by NASA’s Planetary Astronomy Program in Washington. The CIRS instrument and Celeste spectrometer were built at Goddard. JPL is managed by the California Institute of Technology, Pasadena.

To read more about the Fletcher paper, visit: http://www.esa.int/esaSC/SEMLPIMFL8H_index_0.html.

For information about Cassini and this observation, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

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