A Storm on Saturn . ... Credit Copyright: NASA , HST , WFPC 2, Reta Beebe ( NMSU ), D. Gilmore, L. Bergeron ( STScI ) Explanation: The white wisp shown on Saturn 's cloud tops is actually a major storm system only discovered in December of 1994. Saturn 's clouds are composed of primarily hydrogen and helium, but the storm's white clouds are actually ammonia ice crystals that have frozen upon upheaval to the top of the atmosphere. ... NASA Web Site Statements, Warnings, and Disclaimers . ...