NASA | STScI | HubbleSite | 2018 Feb 15
Three billion miles away on the farthest known major planet in our solar system, an ominous, dark storm – once big enough to stretch across the Atlantic Ocean from Boston to Portugal – is shrinking out of existence as seen in pictures of Neptune taken by NASA’s Hubble Space Telescope.
Immense dark storms on Neptune were first discovered in the late 1980s by NASA’s Voyager 2 spacecraft. Since then, only Hubble has had the sharpness in blue light to track these elusive features that have played a game of peek-a-boo over the years. Hubble found two dark storms that appeared in the mid-1990s and then vanished. This latest storm was first seen in 2015, but is now shrinking.
Like Jupiter’s Great Red Spot (GRS), the storm swirls in an anti-cyclonic direction and is dredging up material from deep inside the ice giant planet’s atmosphere. The elusive feature gives astronomers a unique opportunity to study Neptune’s deep winds, which can’t be directly measured.
The dark spot material may be hydrogen sulfide, with the pungent smell of rotten eggs. Joshua Tollefson from the University of California at Berkeley explained, “The particles themselves are still highly reflective; they are just slightly darker than the particles in the surrounding atmosphere.”
Unlike Jupiter’s GRS, which has been visible for at least 200 years, Neptune’s dark vortices only last a few years. This is the first one that actually has been photographed as it is dying. ...
A New Dark Vortex on Neptune - Michael H. Wong et al
- Astronomical Journal 155(3):117 (Mar 2018) DOI: 10.3847/1538-3881/aaa6d6 (pdf)