It the first time a storm has been observed to consume itself in this way anywhere in the solar system, NASA researchers said.
"This Saturn storm behaved like a terrestrial hurricane -- but with a twist unique to Saturn," said Andrew Ingersoll, a member of the imaging team for the Cassini mission orbiting Saturn.
"Even the giant storms at Jupiter don't consume themselves like this, which goes to show that nature can play many awe-inspiring variations on a theme and surprise us again and again."
The storm, first detected in December 2010, spent months wrapping around the planet, throwing off lightning as it wrapped all the way around the globe, scientists said.
Storms on Earth have never run into their own wakes, they said, because they encounter topographic features such as mountains and expend themselves.
But Saturn has no land to stop its storms.
"This thunder-and-lightning storm on Saturn was a beast," Cassini researcher said Kunio Sayanagi at Hampton University in Virginia said. "The storm maintained its intensity for an unusually long time. The storm head itself thrashed for 201 days, and its updraft erupted with an intensity that would have sucked out the entire volume of Earth's atmosphere in 150 days."
This storm was the longest-running of the massive storms that appear to break out in Saturn's Northern Hemisphere once every Saturn year (30 Earth years), the researchers said.