Hubble Captures Neptune's Mysterious Dying Storm—And It Smells Awful

An image of Saturn captured by the Cassini spacecraft. Another NASA project, Hubble, has photographed disappearing storms on Neptune. Photo by NASA/JPL-Caltech/Space Science Institute via Getty Images

Photos taken from NASA's Hubble Space Telescope revealed a new mystery for scientists to crack. The dark storm on Neptune, which was once so vast it spanned the distance from Boston to Portugal, is now shrinking.

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In the 1980s, NASA first discovered dark storms on the planet with its Voyager 2 spacecraft. The large oval-shaped storm was called the Great Dark Spot. Since then, Hubble has given us a better look at the mysterious storms that appear and vanish.

The newest storm was spotted in 2015, and is similar to the gigantic storm swirling on Jupiter, dubbed the Great Red Spot (GRS). Jupiter's particular storm has tumultuous winds that reach up to 400 miles per hour and has been on the planet for more than 150 years. Like the GRS, this storm moves in an anticyclonic direction, which coughs up substances found inside the planet's atmosphere. Analyzing this allows astronomers to study Neptune's winds, as no other measurement tools exist. Scientists believe it could be made of hydrogen sulfide—meaning there's a good chance it smells like rotten eggs.

However, Neptune's storm does differ from the one on Jupiter in that its vortices are short-lived. This new image is the only photograph of a storm captured during its demise. But scientists are puzzled at how they began in the first place.

"We have no evidence of how these vortices are formed or how fast they rotate," Agustín Sánchez-Lavega from the University of the Basque Country in Spain, said in a statement. "It is most likely that they arise from an instability in the sheared eastward and westward winds."

3 billion miles away on Neptune, the farthest known major planet in our solar system, an ominous, dark storm – once big enough to stretch across the Atlantic Ocean from Boston to Portugal – was captured shrinking out of existence by @NASAHubble:

— NASA (@NASA) February 16, 2018

This elusive vortex has also gone rogue, behaving differently than expected.

"It looks like we're capturing the demise of this dark vortex, and it's different from what well-known studies led us to expect," said Michael Wong of the University of California, Berkeley, in a statement. "Their dynamical simulations said that anticyclones under Neptune's wind shear would probably drift toward the equator. We thought that once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity."

Instead, the dark spot faded away instead of vanishing in one big dramatic exit.

We can thank Hubble for the discovery of this baffling phenomenon, according to scientists.

"No facilities other than Hubble and Voyager have observed these vortices. For now, only Hubble can provide the data we need to understand how common or rare these fascinating neptunian weather systems may be," Wong said in a statement.