We know very little about the atmospheres of Uranus and Neptune. Until recently, they hadn't been observed in much detail due to the limited power of our telescopes. Now, thanks to technological advances, astronomers are beginning to learn more about what's going on on these giant planets.
As reported in Geophysical Research Letters, scientists have spent the last year studying images taken by the Hubble Space Telescope that show the formation of a large dark vortex on Neptune. The team has been monitoring the atmosphere for a few years and back in 2015, they spotted bright companion clouds while studying two dark vortices. Given these observations, the team suspects the largest dark storms originate much deeper in the planet.
This is not the first dark spot that's been seen on Neptune. So far researchers have spotted six. Neptune has only been visited by a spacecraft once when Voyager 2 briefly flew past it in 1989. In that encounter, the spacecraft snapped images of two dark storms blotching the atmosphere of the dark blue planet. Surprisingly, Hubble observations just five years later didn’t detect them. They had disappeared.
“It was certainly a surprise,” lead author Dr Amy Simon, from NASA’s Goddard Space Flight Center, said in a statement. “We were used to looking at Jupiter’s Great Red Spot, which presumably had been there for more than 100 years. We have so little information on Uranus and Neptune.”
The new dark storm is similar in size to the "Great Dark Spot" seen by Voyager 2, making its diameter a little larger than our own planet's. The team used computer models to work out how such a storm could be produced on the planet. The simulation showed that there's a link between the storms and the bright clouds, suggesting that the deeper the storm the brighter the clouds.
The modeling and observations also gave the researchers an idea of how long these dark vortices last. They form every four to six years and tend to have a maximum lifespan of six years, although two years is the more likely number. Simon and her colleagues Andrew Hsu and Michael Wong have published a paper outlining this finding in The Astronomical Journal.
Neptune is often seen as a great model for many of the exoplanets we have discovered so far. Understanding its properties is very important if we want to construct realistic evolutionary scenarios for planets orbiting distant stars.
