Everything about The Great Dark Spot totally explained
The
Great Dark Spot (GDS-89) was a dark spot on
Neptune similar in appearance to
Jupiter's Great Red Spot. It was detected in 1989 by
NASA's
Voyager 2 probe. Although it appeared similar to Jupiter's spot, which was an
anticyclonic storm, it's believed that the Great Dark Spot was a relatively cloud-free region.
Characteristics
The spot was relatively the same size as
Earth itself, and was very similar in appearance to
Jupiter's
Great Red Spot. At first it was thought to be a
storm, like the Great Red Spot, but closer observation revealed it to be a dark,
elliptically-shaped depression in Neptune. Around the Great Dark Spot, winds were measured blowing up to 2,400 kilometers (1,500 miles) an hour, the fastest in our Solar System. The Great Dark Spot is thought to be a hole in the
methane cloud deck of
Neptune, similar to the holes in the
ozone layer on Earth. In many images of Neptune, the spot has been observed at different sizes and shapes.
The Great Dark Spot generated large white clouds similar to high-altitude
cirrus clouds found on
Earth. Unlike cirrus clouds, however, which are composed of crystals of ice, Neptune's cirrus clouds are made up of crystals of frozen
methane. And while cirrus clouds usually form and then dissolve within a period of a few hours, the clouds in the Great Dark Spot hadn't dissolved after 36 hours, or two rotations of the planet.
Disappearance
When the spot was to be photographed again in 1994 by the
Hubble Space Telescope, the spot had disappeared completely, leaving astronomers to believe that it had either been covered up or vanished. However, an almost identical spot emerged in Neptune's northern
hemisphere. This new spot, called the Northern Great Dark Spot (NGDS), has remained visible for several years.
Further Information
Get more info on 'Great Dark Spot'.
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