Hubble Space Telescope Sees Shrinking Dark Spot on Neptune

Hubble Space Telescope Sees Shrinking Dark Spot on Neptune

First spotted by Voyager 2, Neptune's ominous storms have been a mystery since the late 1980s.

And it probably stinks: "The dark spot material may be hydrogen sulfide, with the pungent smell of rotten eggs".

This includes two dark storms that appeared in the 1990s but suddenly vanished, and now the massive storm identified in 2015 is shrinking.

A darkly colored storm on Neptune that's the diameter of the Atlantic Ocean is shrinking. Hubble and Voyager are the only scientific instruments able to observe Neptune's storms.

The storm shares similar characteristics with Jupiter's storm as it swirls in an anti-cyclonic direction pulling up huge amounts of material from deep inside the ice giant's atmosphere and has been important to astronomers because it gives us a glimpse of the planet's deep winds. Only five of these dark vortices have been discovered on Neptune, and this most recent one, named SDS-2015, can only be detected and tracked by the same thing that found it.

Since 2015, astronomers have been following a dark vortex the size of China swirling over Neptune, the solar system's outermost planet. "It is most likely that they arise from an instability in the sheared eastward and westward winds", said Sánchez-Lavega.

Such vortices are frequently forming in the Neptune's atmosphere when clouds of air and gas twist and freeze.

The storm's "particles themselves are still highly reflective; they are just slightly darker than the particles in the surrounding atmosphere", Joshua Tollefson from the University of California at Berkeley said in a statement.

Scientists have made some guesses about how a storm would behave when it dissipated.

"Many questions remain as to how dark vortices originate, what controls their drift and oscillation, how they interact with the environment, and how they eventually dissipate", according to the paper.

"We thought that once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity", informed Michael Wong of the University of California at Berkeley. Instead, the storm seems like it's just fading into nothing as it moves toward Neptune's south pole and not the planet's equator as expected, NASA said.

Neptune might not be as big as Jupiter or adorned with the rings like Saturn, but it is well distinguished from all the other planets in our solar system by its incredibly powerful winds, which at times even reach supersonic speeds, according to NASA's press-release. This allows Neptune's vortex to be a shiftless drifter, changing its "traffic lanes" in ways that are hard to anticipate.