So big it could engulf several Earths, Jupiter’s Great Red Spot is a gigantic storm that has been raging for centuries with winds blasting at over 600 kilometres per hour. But it has a rival: astronomers have discovered that Jupiter has a second Great Spot, this time a cold one.
In the polar regions of the planet, astronomers using the CRIRES instrument on ESO's Very Large Telescope, along with other facilities, have found a dark spot in the upper atmosphere (below the aurora to the left) about 200 °C cooler than its surroundings. Aptly nicknamed the “Great Cold Spot”, this intriguing feature is comparable in size to the Great Red Spot — 24 000 km across and 12 000 km tall. But data taken over 15 years show that the Great Cold Spot is much more volatile than its slowly-changing cousin. It changes dramatically in shape and size over days and weeks — but never disappears, and always stays roughly in the same location.
The Great Cold Spot is thought to be caused by the planet’s powerful aurorae, which drive energy into the atmosphere in the form of heat that flows around the planet. This creates a cooler region in the upper atmosphere, making the Great Cold Spot the first weather system ever observed to be generated by aurorae.
Image Credit: ESO/T. Stallard
Explanation from: https://www.eso.org/public/images/potw1716a/