<P> When the spot was to be photographed again in November 1994 by the Hubble Space Telescope , it had disappeared completely , leaving astronomers to believe that it has either been covered up or vanished . The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer visible as a dark feature . Dark spots may dissipate when they migrate too close to the equator , or possibly through some other unknown mechanisms . </P>
<P> When the spot was to be photographed again in November 1994 by the Hubble Space Telescope , it had disappeared completely , leaving astronomers to believe that it has either been covered up or vanished . The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer visible as a dark feature . Dark spots may dissipate when they migrate too close to the equator , or possibly through some other unknown mechanisms . </P>
what happened to the great dark spot on neptune
what happened to the great dark spot on neptune
either been covered up or vanished
either been covered up or vanished