Great Dark Spot
When pictures were going to be taken of the Great Dark Spot again in November 1994 by the Hubble Space Telescope, it had gone away completely, leaving astronomers to believe that it had either been covered up or that it had just disappeared. The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer able to be seen as a dark feature. Dark spots may disappear when they move too close to the equator or possibly through some other unknown way.