Astronomers have been watching this northern-hemisphere storm since December 2010, when a bright plume of gas and ice bubbled up to the surface of the gaseous sphere that makes up Saturn.

The disturbance has since expanded by riding easterly winds blowing at up to about 220 miles an hour (100 meters a second). But until now very little has been known about the workings of the storm, its depth, and how it affects the ringed planet.