An unusually bright storm system nearly the size of Earth has been spotted in the atmosphere of Neptune, baffling researchers because it is located near the ice giants equator.

This image from the Keck Telescope shows an extremely bright, nearly circular storm system near Neptunes equator. Image credit: Ned Molter & Imke de Pater, University of California, Berkeley / C. Alvarez, W. M. Keck Observatory.

This giant storm system is unusually bright and is about 5,600 miles (9,000 km) in length, or one-third the size of Neptunes radius, spanning at least 30 degrees in both latitude and longitude.

The storm was discovered earlier this year by Ned Molter, a graduate student at the University of California, Berkeley, in images taken by an optical/infrared telescope at W. M. Keck Observatory on Maunakea, Hawaii.

Seeing a storm this bright at such a low latitude is extremely surprising. 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, Molter said.

He observed the system getting much brighter between June 26 and July 2.

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 Professor Imke de Pater, also from the University of California, Berkeley.

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

At first, the scientists thought the storm system was the same Northern Cloud Complex seen by the NASA/ESA Hubble Space Telescope in 1994, after the iconic Great Dark Spot, imaged by NASAs Voyager 2 in 1989, had disappeared.

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

Images of Neptune (upper row June 26, lower row July 2) revealed an extremely bright storm system near Neptunes equator (labeled cloud complex in the upper figure). Image credit: Ned Molter & Imke de Pater, University of California, Berkeley / C. Alvarez, W. M. Keck Observatory.

A massive, high-pressure, dark vortex system anchored deep in Neptunes atmosphere may be whats causing the colossal cloud cover.

As gases rise up in a vortex, they cool down. When its temperature drops below the condensation temperature of a condensable gas, that gas condenses out and forms clouds, just like water on Earth. On Neptune we expect methane clouds to form.

As with every planet, winds in Neptunes 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.

This big vortex is sitting in a region where the air, overall, is subsiding rather than rising. Moreover, a long-lasting vortex right at the equator would be hard to explain physically, Professor de Pater said.

If it is not tied to a vortex, the system may be a huge convective cloud, similar to those seen occasionally on other planets like the huge storm on Saturn that was detected in 2010.

Although one would also then expect the storm to have smeared out considerably over a weeks time.

This shows that there are extremely drastic changes in the dynamics of Neptunes atmosphere, and perhaps this is a seasonal weather event that may happen every few decades or so, Professor de Pater said.

Link:

Giant, Extremely Bright Storm System Spotted in Neptune's Atmosphere - Sci-News.com