NASA's Voyager 2 space probe captured the first image of Neptune's Great Dark Spot in 1989. This massive storm system appeared as a dark, elliptical shape within the planet's southern hemisphere and measured roughly the same size as Earth itself.
Winds surrounding the Great Dark Spot reached speeds of up to 2,100 kilometers per hour. These measurements represent the fastest recorded winds anywhere in the Solar System.
Astronomers expected to photograph the Great Dark Spot again when Hubble Space Telescope observations began in November 1994 but found the feature had vanished completely from view. Some theories suggest the storm migrated too close to the equator where Coriolis forces weaken and dissipate it while others propose the dark hole became covered by rising companion clouds blocking the blue light used for detection.
This latest storm measured approximately 4,600 miles across making it larger than the Atlantic Ocean. It suddenly reversed its southward motion in August 2020 contrary to projections about its eventual demise at the equator.
NASA received proposals for spacecraft missions including Trident and Neptune Odyssey to study the planet further. Trident was proposed in 2021 as a discovery mission targeting Neptune and its moon Triton while Neptune Odyssey aims for a launch date around 2033 as a flagship orbiter concept.