For the first time ever, scientists were able to observe the birth and development of a new Great Dark Spot on Neptune.
Using images from the Hubble Space Telescope, a team from NASA's Goddard Space Flight Center and the University of California, Berkeley watched as companion clouds began to appear on the face of the ice giant in 2015 and witnessed the new dark spot emerge in 2018.
The images also help scientists better understand the inner workings of the ice giants within the solar system and similar planets across the universe.
Their findings appear in the American Geological Union's journal Geophysical Research Letters.
Neptune's Mysterious Storms
In 1989, when the Voyager 2 flew past Neptune, it captured the image of two dark vortices on the southern hemisphere of the ice giant. Scientists dubbed the storms "The Great Dark Spot" and "Dark Spot 2."
In 1994, the Hubble Space Telescope took sharp images of Neptune. Scientists discovered that both giant storms have dissipated.
"It was certainly a surprise," said Amy Simon, a planetary scientist at NASA. "We were used to looking at Jupiter's Great Red Spot, which presumably had been there for more than a hundred years."
Over the years, the Hubble Space Telescope has witnessed several other dark spots appear and disappear on the face of Neptune but the phenomenon is still poorly understood.
A Great Dark Spot
The team came across the new Great Dark Spot in the southern hemisphere by accident. They were actually monitoring another, smaller storm in Neptune from 2015 when the new one emerged.
While analyzing images from the Hubble Space Telescope, the team saw small and white clouds forming in the region where the dark spot would later appear. They said that the clouds were made up of methane ice crystals, that is why they look bright and white.
The presence of these clouds suggests that the storms originate from a deeper region of the planet's atmosphere than originally thought.
The team also suspected that a new dark vortex appears on Neptune every four to six years. Each storm lasts up to six years before it disappears, although a two-year lifespan is more likely, according to the study.
The study also compared the Great Dark Spots of Neptune to Jupiter's famous and persistent Great Red Spot which has been raging for hundreds of years. The giant storm in Jupiter is accompanied by thin jet streams that keep it from breaking apart and places it in one set path.
However, wind in Neptune has a wider band that allows the storms to drift across latitudes.
Scientists hope to continue observing the storms in Neptune to learn more about ice giants within and outside the solar system.
"If you study the exoplanets and you want to understand how they work, you really need to understand our planets first," stated Simon. "We have so little information on Uranus and Neptune."