Facts about Neptune's Dark Spots
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A new dark spot discovered near Neptune's north pole in 2018 marked the first time such a feature had been observed in the planet's northern hemisphere.
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Methane in Neptune's upper atmosphere absorbs red light, giving the dark spots their distinctive deep blue coloration in visible light observations.
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Smaller dark spots on Neptune, designated as dark spot 1, persisted for approximately 4-6 years during observations between 1989 and 1995, outlasting the Great Dark Spot's brief existence.
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Dark spot wind speeds on Neptune can reach 2,100 kilometers per hour, making them among the fastest atmospheric winds measured in our solar system.
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Neptune's dark spots are anticyclonic high-pressure systems composed of methane ice crystals that form at altitudes approximately 50 kilometers above the planet's cloud tops.
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Bright companion clouds called scooter clouds travel alongside Neptune's dark spots at speeds reaching 2,400 kilometers per hour, moving faster than the dark spots themselves.
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Around 40 percent of Neptune's dark spots disappear within 1-2 years, indicating these anticyclonic storms are transient atmospheric features unlike Jupiter's Great Red Spot.
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Hubble observations revealed a second dark spot, designated D2, in Neptune's southern hemisphere during 1994 with winds exceeding 2,100 kilometers per hour.
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The Great Dark Spot observed by Voyager 2 in 1989 had vanished completely by the time the Hubble Space Telescope photographed Neptune in 1994, suggesting these storms persist for only years rather than decades.
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In 1989, Voyager 2 discovered Neptune's Great Dark Spot, a storm system roughly the size of Earth rotating counterclockwise every 16 days.