The storm erupted in December 2010 with a burp, Hesman said. The Cassini spacecraft, orbiting Saturn, picked up the information and sent it back to Earth.
"The reason we call it the burp is, essentially, the storm erupted from below and all this energy moved into the stratosphere," she said.
Scott Edgington is deputy project scientist with the Cassini spacecraft. In an interview Thursday with The Times he described the storm and the instrument that recorded it for history.
The storm grew over the course of about nine months, he said, likening it to "a boiling pot of water"; material bubbled up into Saturn's stratosphere over the course of time.
Cassini analyzed the storm using its Composite Infrared Spectometer (CIRS). Edgington said CIRS measures temperature and the abundance of different kinds molecules.
"That instrument saw a drastic rise in temperature, about 80 degrees Kelvin," or 150 degrees Fahrenheit, above normal, he said, "which is unprecedented for anything we've ever seen in the solar system."
Cassini also detected that the atmospheric burp brought up an astounding quantity of a molecule that was thought to be on Saturn but not on such a vast scale: ethylene.
"What caused this molecule to be present in such huge quantities is unknown at this time," Edgington said. "Our experience on Earth is so different from the chemistry happening on Saturn -- there's nothing to compare it to."
Similar storms, such as the Great White Spot storms, occur annually on the planet, though one year on Saturn is 30 years on Earth.
The next time this type of storm rolls around on Saturn, Hesman said, scientists probably will not be able to document it in the historic way they have what's being called the 2010 Saturn Northern Storm. By then, Cassini -- which sends back reams of data -- wil be gone.
"We did not have the technology the last time this type of storm erupted," said Hesman, who is lead author of a study on the Saturn storm and its aftermath that will be published in the Nov. 20 issue of the Astrophysical Journal.
"This is our first really thorough historical record," she said. "In generations to come, when they study storms on Saturn, this is what they'll come back to."
In 2017, Cassini will plunge into Saturn.
And that will be the end for a spacecraft that NASA says has logged more than 3.8 billion miles in space. Beginning in November 2016, its orbits will take it ever closer to Saturn, until on Sept. 15, 2017, it enters the planet's atmosphere, where the intense pressure will crush and vaporize the craft.
Video: ESA/C. Carreau