NASA’s Hubble Space Telescope detected a dark vortex in Neptune’s atmosphere on May 16. The dark spot measures 3,000 miles or 4,800 kilometers across.

The finding marks the first time the dark vortex is seen in the 21st century but this was actually the third time astronomers spotted the dark spot. The first time was by the Voyager 2 in 1989 and the second detection was in 1994, which was also made by the Hubble Space Telescope.

Astronomers explain that the dark vortices are high-pressure systems that are formed when gas clouds and air in Neptune’s atmosphere start spinning around and freeze. Dark vortices usually have bright clouds accompanying them, which are formed when the air is disrupted and pushed above the dark vortex.

dark vortex

Neptune’s dark vortex. Credit: NASA, ESA, and M.H. Wong and J. Tollefson (UC Berkeley)

“Dark vortices coast through the atmosphere like huge, lens-shaped gaseous mountains,” says lead researcher and astronomer Mike Wong from University of California at Berkeley. “And the companion clouds are similar to so-called orographic clouds that appear as pancake-shaped features lingering over mountains on Earth.”

In July 2015, scientists predicted that another dark vortex was forming in Neptune when they saw bright clouds in the planet. Only the Hubble telescope is equipped to see a dark vortex, which can only be seen at blue wavelengths.

Then in September 2015, the Hubble Space Telescope project called the Outer Planet Atmospheres Legacy (OPAL) program spotted a dark spot close to bright clouds. This confirmed the presence of the dark vortex.

All dark vortices are not exactly alike. Scientists explain each vortex can vary in shape, size and stability, which means they could speed up or slow down. Unlike the anticyclones in Jupiter, Neptune’s vortices come and go much quickly. Normally, the storms in Jupiter grow within several decades.

According to Joshua Tollefson, a PhD student at UC Berkeley, more investigations are still needed to further understand the true nature of these dark vortices and their origins, how they impact Neptune’s environment, how they disappear as well as the environmental factors that control their movements.   Moreover, digging deep into how a dark vortex evolves will provide more data about this event and Neptune’s atmosphere.