Astronomers using NASA’s Hubble Space Telescope say a mysterious dark storm on Neptune has suddenly changed its direction, which they say they have never seen before.
The storm, which is wider than the Atlantic Ocean, has been raging in the northern hemisphere of the gas giant since at least 2018, and is slowly moving toward the planet’s equator where similar storms are expected to scatter.
But instead of slowing down to its death, to the astonishment of the audience, the vortex suddenly changed direction and doubled north again by August 2020.
Hubble, the only telescope with sharpness and sensitivity to the visible spectrum of light to observe these elusive features, was the first to observe this type of atmospheric behavior.
Adding to the mystery, in January of this year Hubble found another small dark spot that appeared near the big storm. Scientists suspect it may have been part of a giant vortex that broke apart before it disappeared.
“We’re excited about these observations because this little dark piece is part of the process of disrupting dark space,” said Dr. Michael Wong of the University of California, Berkeley.
“This is a process that has never been noticed. We have seen some other dark spots disappear, they are gone, but we have not seen anything disruptive as predicted in computer simulations,” Dr. Wong added.
The largest hurricane to cross 4,600 miles (7,400 km) – more than the distance from London to Miami – was the fourth dark spot Hubble observed on Neptune since 1993.
Two other storms were detected by the Voyager 2 spacecraft in 1989, but disappeared while Hubble was orbiting them.
“How these storms form is still a mystery, but this latest giant vortex is the best ever studied,” NASA said.
“The dark appearance of a storm may be due to a high dark cloud layer, and this may tell astronomers about the vertical structure of the storm.
“Another unusual feature of the dark space is the absence of bright sub-clouds around it, which were in the Hubble images taken when the vortex was discovered in 2018,” NASA added.
“Clouds disappear when the vortex stops traveling to the south. Bright clouds form when the airflow is disturbed and turned upwards on the vortex, causing gases to freeze into methane ice crystals.
“The lack of clouds may reveal information about how dot points form,” the researchers added.