Astronomers Catch the Formation of a Dark Vortex on Neptune

Cristina Cross
March 28, 2019

For example, photos captured by the space telescope in 1994 revealed that the two tempests seen by Voyager 2 had dissipated, revealing that Great Dark Spots don't last very long, at least by giant-planet standards.

Computer models of Neptune's atmosphere showed that the deeper the storm, the brighter its companion clouds.

Scientists have seen a total of six dark spots on Neptune over the years.

The Hubble telescope was launched on April 24, 1990, via the space shuttle Discovery from Kennedy Space Centre in Florida. They discovered that the clouds were the most bright in 2016 and 2017, before the new great dark spot became visible in 2018.

They studied the clouds that showed up two years before this Great Dark Spot deal, and they have concluded that these dark spots come from the more profound atmosphere of Neptune.

By peering through the lens of the Hubble Space Telescope, NASA researchers have captured one of Neptune's storms at is was brewing. The Hubble image shows a new dark storm (top center).

Dr. Simon and co-authors also used images from Hubble and Voyager 2 to pinpoint how long Neptunian storms last and how frequently they occur. It is about 13,000 km by 6,600 km in size - as large along its longer dimension as the Earth. The images also help scientists better understand the inner workings of the ice giants within the solar system and similar planets across the universe.

"It was certainly a surprise", said Amy Simon, first author of the paper and a planetary scientist at NASA.

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Over the past few decades, scientists have observed six dark spots on Neptune. They were surprised to see hat the two giant storms had disappeared. So while astronomers can't predict for sure where a storm will form, they can look back and trace its history, even before the dark spot itself became visible. That is unlike Great Red Spot on the Jupiter which kept nearly still in latitude for at least 350 years. Then, in 2018, a new Great Dark Spot splashed across its surface; it was almost identical in size, shape, and position as the one seen in 1989, the team reports, right where those clouds used to be.

Astronomers were studying Hubble Space Telescope images of a relatively small Neptune maelstrom that formed in 2015 when they noticed bright white clouds forming in a different locale on the ice giant.

'We were so busy tracking this smaller storm from 2015, that we weren't necessarily expecting to see another big one so soon, ' Simon said.

According to NASA, these clouds are made up of methane ice crystals and sit high in the atmosphere above the darker material.

But a year ago, they spotted a new dark spot just north of the equator. The storms typically hover between westward equatorial wind jets and eastward-blowing currents in the higher latitudes before strong winds pull them apart.

The team's latest evidence suggests that new storms crop up on Neptune every four to six years with each lasting as many as six years. "We have never directly measured winds within Neptune's dark vortices, but we estimate the wind speeds are in the ballpark of 328 feet (100 meters) per second, quite similar to wind speeds within Jupiter's Great Red Spot", said Wong.

Michael H. Wong, Andrew I. Hsu: University of California Berkeley, Berkeley, California, U.S.A.

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