Neptune has one of the strangest weather conditions in the solar system. The eighth planet from the sun holds the record for the fastest winds observed on any world, with speeds cutting through the atmosphere at a speed of 1,100 miles per hour, or 1.5 times the speed of sound. Scientists are still not sure why the atmosphere is so tumultuous. Their last glimpse of Neptune gave even more cause for confusion.
© NASA, ESA, STScI, MH Wong, LA Sromovsky and PM Fry
The Hubble Space Telescope identified a storm in 2018, a dark spot about 4,600 miles in diameter. Since then, it appears to have drifted towards the equator, but then north again, according to the latest Hubble observations. It also has a smaller companion nicknamed Dark Spot Jr., which scientists believe is a chunk that broke off the main storm. These inky black vortices stand out against the planet’s dazzling cerulean blue, but while dazzling to behold, their lifespans are short, making them even more challenging to study.
Charging error
This isn’t the first time that Neptune’s dark spots have acted so strangely. When the Voyager 2 spacecraft flew past the planet in 1990 (still the only spacecraft to do this), it observed two storms. One of these was the original dark spot, a large vortex the size of the Earth. It also had a companion, a smaller, fast-moving storm nicknamed Scooter. The first dark spot observed also seemed to move south and then north again.
“When we followed the great dark spot with Voyager, we saw it oscillate up and down in longitude,” said Heidi Hammel, a member of the Voyager 2 spacecraft imaging team and currently the vice president of science at the Association of Universities for research in astronomy. “We had enough time on Voyager so that we could monitor the position for about four to five months leading up to the flyby. That storm was huge, a great monster, “the size of the Earth.
But by the time the Voyager team got time with the Hubble telescope to re-observe the storms, some four years later, they were gone. Astronomers estimate that the average lifespan of a Neptune storm is anywhere from two to five years, and the lifespan may also depend on its size. That’s a contrast to Jupiter’s Great Red Spot, our outer solar system’s other best-known storm, which is sometimes shrinking but has been churning constantly for at least hundreds of years.
Neptune’s dark vortices plunge deep into the planet – imagine them as the canopy of a very tall tree with roots stretching to the core of the icy world. This long connection can move the storm in all directions, allowing it to drift south with the wind or pull it north again. But as these great storms drift south to the planet’s equator, where the wind fields are even stronger, they can be torn apart.
Because astronomers only take a picture once a year to use Hubble to look at Neptune, it’s hard to really track the temperamental atmosphere. So by the time scientists discover new storms, we’ll only have a few chances to observe them before they disappear.
“This whole idea of them disappearing is one of the more puzzling aspects of them,” said Dr. Hammel.
Until humans can orbit the planet to better understand the life cycle of these storms, there will be more questions than answers about this blue beauty. Will Dark Spot and Dark Spot Jr. survive? Check back in 2021 to find out.
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