Storm on Saturn, Cassini images. This vortex formed in December 2010 from a giant storm on Saturn, slowly dissipating between January and October 2011. The first image (upper left) shows the most turbulent activity (11 January 2011). At the time, it was the largest vortex ever observed in Saturn's troposphere, and measured some 12,000 kilometres across. It drifted west during March and April. The storm that caused the vortex merged with it by mid-June, with the merged structure in the July and August images. By October (lower right) the vortex had nearly faded away. The colours show cloud altitude: red (lowest), green (intermediate) and blue (highest).