A Giant Storm on Neptune Is Disappearing as Hubble Telescope Watches

A dark storm on Neptune, once big enough to reach from Boston to Portugal, is dwindling to nothing as the Hubble Space Telescope keeps watch.

When NASA's Voyager 2 spacecraft flew by Neptune in 1989, it observed large, dark storms flying through the distant planet's atmosphere. Since then, scientists have monitored Neptune using the Hubble Space Telescope and seen new storms develop.

But unlike Jupiter's Great Red Spot, which has been roiling for at least two centuries, the storms brewing on the windy planet Neptune come and go in just a few years — and now, for the first time, researchers have seen one begin to disappear, NASA officials said in a statement. [The Amazing Blue Planet Neptune in Photos]

The giant, dark storms on Neptune are impermanent features on the distant planet.
Credit: NASA/JPL

"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," Michael Wong, a researcher at the University of California at Berkeley and lead author on the new work, said in the statement. Previous simulations suggested that the vortex would drift toward the planet's equator, and "once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity."

But instead, it drifted toward the planet's south pole and is quietly fading away. The vortex was 3,100 miles (5,000 kilometers) across the long axis when Hubble spotted it in 2015, and now it's down to 2,300 miles (3,700 km) across.

The Hubble Space Telescope took this series of images of Neptune over two years, showing a dark vortex on its surface slowly shrinking from 3,100 miles (5,000 km) across the long axis to 2,300 miles (3,700 km) across.
Credit: M.H. Wong and A.I. Hsu (UC Berkeley)/NASA/ESA

The planet's anticyclones, like this dark storm, pull up darker material from deeper inside Neptune as it spins — it could be hydrogen sulfide, which smells like rotten eggs, NASA officials said — carried along by three wind jets circling the planet: one going west at the equator, and two going east near each of the poles. Neptune's powerful winds are the fastest ever detected in the solar system and can reach supersonic speeds — and understanding the planet's storms can reveal to researchers just how deep they go.

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

The new work was detailed Feb. 15 in the Astronomical Journal.

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Neptune is the most distant full-fledged planet in the solar system (though some Pluto fans would beg to differ). Test your knowledge of this strange and frigid world.