资源环境科技发展态势分析平台

For the first time, Hubble Space Telescope visible-wavelength imaging shows the formation history of a dark vortex on Neptune. A new northern Great Dark Spot (NDS-2018) was discovered in September and November 2018 images, spanning roughly 12 degrees of latitude and 27 degrees in longitude (11,000 x 5,000 km) at 23 degrees N planetographic latitude. NDS-2018 is similar in size, shape, and longitudinal drift rate as the Voyager 2 Great Dark Spot near 22 degrees S. NDS-2018 was prominent in blue-wavelength November 2018 images and drifted at 2.46 degrees/hr westward. Yearly global maps demonstrate possibly related cloud activity in prior years. The drift rate and formation history of the dark vortex indicates a deep origin. We estimate that the north-south gradient in zonal wind speed is almost 4 times larger at the depth of the dark vortex, compared with cloud-tracked zonal winds.

Plain Language Summary In 2018, a new Great Dark Spot was discovered on Neptune, nearly identical in size and shape as the one observed by Voyager 2 in 1989. The spot is in the Northern Hemisphere and is drifting westward more slowly than the surrounding winds. Dark spots can only be identified in visible light, because of their strong absorption at blue wavelengths, and only the Hubble Space Telescope has sufficient spatial resolution to detect them. A search of global Hubble Neptune images from 2015 through 2017 reveals smaller clouds present at locations consistent with this storm, meaning, it may take many years to form. If so, it may originate from much deeper in the atmosphere than previously thought. Future computer simulations of Neptune's dark storms can be constrained by these new observations to teach us more about deep atmosphere conditions and processes on all the giant planets.