Massive storm spotted on Neptune is as big as Earth and 9,000 kilometres in length

A massive storm system about the size of our Earth has been observed by the astronomers near the equator of Neptune. The storm has been spotted in a region where no bright cloud has ever been seen before.

The gigantic storm system is about 9,000 kilometres in length or one-third the size of Neptune’s radius. It spans at least 30 degrees in both latitude and longitude.

"Seeing a storm this bright at such a low latitude is extremely surprising," said Molter, who spotted the storm near Neptune's equator during a dawn test run of twilight observing at W M Keck Observatory on Maunakea, Hawaii.

"Normally, this area is really quiet and we only see bright clouds in the mid-latitude bands, so to have such an enormous cloud sitting right at the equator is spectacular," said Molter.

"Historically, very bright clouds have occasionally been seen on Neptune, but usually at latitudes closer to the poles, around 15 to 60 degrees north or south," said Imke de Pater, a professor at UC Berkeley.

"Never before has a cloud been seen at or so close to the equator, nor has one ever been this bright," said de Pater.

de Pater at first thought it was the same Northern Cloud Complex spotted by NASA’s Hubble Space Telescope back in 1994, after the iconic Great Dark Spot, imagined by Voyager 2 in 1989 had disappeared. 

However, de Pater said measurements of its locale do not match, signalling that this cloud complex is different from the one Hubble first saw more than two decades ago.

The gases cool down when they rise up in a vortex. That gas condenses out and forms clouds just like water on Earth when its temperature drops below the condensation temperature of a condensable gas. However, methane clouds form on Neptune.

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As with every planet, winds in Neptune's atmosphere vary drastically with latitude, so if there is a big bright cloud system that spans many latitudes, something must hold it together, such as a dark vortex. Otherwise, the clouds would shear apart, researchers said.

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(With inputs from PTI)