Saturday, May 1, 2021

The Great Dark Spot

Most of you will have heard of the Great Red Spot, the huge storm in the Jovian atmosphere.

However, Jupiter is not the only planet to host vortices of considerable size: when the Voyager 2 probe reached Neptune in 1989 it found itself in front of something very similar to the Great Red Spot. This blue storm was dubbed the Great Dark Spot.

The images taken by Voyager 2 allowed to accurately determine its size, which turned out to be 13000 x 6000 km. At the edge of the storm, the probe measured winds blowing at a speed of 2100 km/h, the fastest recorded in the history of the Solar System.

Unfortunately, Voyager 2's flyby was too fast to study the storm's temporal evolution.

When the Hubble Telescope tried to observe Neptune five years later it was found that the Great Dark Spot had disappeared.

In 2016 on the opposite hemisphere of Neptune, a new storm similar to that of the 1990s reappeared. By studying the temporal evolution of the latter, astronomers were able to partially reconstruct the characteristics of the Great Dark Spot.

Neptunian storms are currently believed to be holes in the outermost methane layer, through which it is possible to see the atmospheric layers below.

To know more about the formation and evolution of these atmospheric structures, however, new data will be needed, possibly obtained from probes orbiting Neptune.

Credit: NASA.

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