© Hubblesite
New images obtained on May 16, 2016, by NASA's Hubble Space Telescope confirm the
presence of a dark vortex in the atmosphere of Neptune. Though similar features were seen during the Voyager 2 flyby of Neptune in 1989 and by the Hubble Space Telescope in 1994, this vortex is the first one observed on Neptune in the 21st century.
The discovery was announced on May 17, 2016, in a Central Bureau for Astronomical Telegrams (CBAT) electronic telegram by University of California at Berkeley research astronomer Mike Wong, who led the team that analyzed the Hubble data.
Neptune's dark vortices are high-pressure systems and are usually accompanied by bright "companion clouds," which are also now visible on the distant planet. The bright clouds form when the flow of ambient air is perturbed and diverted upward over the dark vortex, causing gases to likely freeze into methane ice crystals. "Dark vortices coast through the atmosphere like huge, lens-shaped gaseous mountains," Wong said. "And the companion clouds are similar to so-called orographic clouds that appear as pancake-shaped features lingering over mountains on Earth."
Beginning in July 2015, bright clouds were again seen on Neptune by several observers, from amateurs to astronomers at the W. M. Keck Observatory in Hawaii. Astronomers suspected that these clouds might be bright companion clouds following an unseen dark vortex. Neptune's dark vortices are typically only seen at blue wavelengths, and only Hubble has the high resolution required for seeing them on distant Neptune.
Comment: For more on the rise in extreme weather phenomena, check out Earth Changes and the Human Cosmic Connection.