June 24, 2016 10:10 AM EDT

NASA’s Hubble Space Telescope confirmed a dark vortex in Neptune’s atmosphere that spans the width of the continental United States.

The telescope obtained images on May 16 which confirmed the presence of this vortex, the first one observed in the 21st century. Hubble announced this discovery to the public Thursday.

Neptune’s dark vortices are high-pressure systems that are usually accompanied by bright “companion clouds.” These pancake-shaped clouds form when the flow of ambient air is diverted upward over the dark vortex, which causes gases to likely freeze into methane ice crystals. They resemble clouds that sometimes form over Earth’s mountains.

“Dark vortices coast through the atmosphere like huge, lens-shaped gaseous mountains,” University of California at Berkeley research astronomer Mike Wong, who led the team analyzing the Hubble data, said in a statement.

Several observers started seeing bright clouds on Neptune in July 2015, and astronomers suspected they might be companion clouds accompanying a dark vortex. The Outer Planet Atmospheres Legacy (OPAL) program, a Hubble Space Telescope project, revealed a dark spot near the clouds in September 2015. The new Hubble images confirmed it and allowed the research team to create a map of the vortex and its surroundings.

Similar features have been observed by the Voyager 2 flyby of Neptune in 1989 and by the Hubble Space Telescope in 1994.

More Must-Reads From TIME

Contact us at letters@time.com.

You May Also Like