Hubble sees Neptunes dark storm die (earthsky.org)

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By Deborah Byrd in Space | February 18, 2018

In the 1980s, Voyager 2 discovered a dark storm in Neptune’s dense atmosphere, and now the Hubble Space Telescope is tracking Neptune’s storms. More in this NASA video.

Jupiter’s Great Red Spot is known to be a giant hurricane that’s raged for centuries at least. Likewise, the 8th planet Neptune has great storms, but they’re tougher to see and track because Neptune is smaller and farther away at some 3 billion miles (5 billion km). In the late 1980s, the Voyager 2 spacecraft discovered huge dark storms in Neptune’s dense atmosphere. Since then, only the Hubble Space Telescope has had the capabilities to track these elusive features over the years. Hubble found two dark storms on Neptune that appeared in the mid-1990s, then vanished. It found Neptune’s latest storm in 2015, and now it’s watching that storm shrink.

The first storms seen by Hubble on Neptune were about the average width of the Atlantic Ocean (about 3,000 miles or 5,000 km). The darkness might come from hydrogen sulfide, researchers say, which has the pungent smell of rotten eggs. Joshua Tollefson of the University of California at Berkeley studies these storms. He said of the material inside the storms:

The particles themselves are still highly reflective; they’re just slightly darker than the particles in the surrounding atmosphere.

As with Jupiter’s Great Red Spot, storms on Neptune swirl in an anti-cyclonic direction and dredge up material from deep inside the ice giant planet’s atmosphere. NASA said:

The elusive feature gives astronomers a unique opportunity to study Neptune’s deep winds, which can’t be directly measured.

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more: http://earthsky.org/space/neptune-dark-storm-spot-die-voyager-hubble
https://archive.stsci.edu/prepds/opal/