Dubbed the ‘Great Cold Spot’, scientists said the dark spot is created by the powerful energies exerted by the great planet’s polar aurorae.
The dark expanse is up to 24,000 km in longitude and 12,000 km in latitude. It's in the gas giant’s thin high-altitude thermosphere - that is around 200K (Kelvin) cooler than the hot surrounding atmosphere, which can range in temperature between 700K (426ºC) and 1000K (726ºC).
“This is the first time any weather feature in Jupiter's upper atmosphere has been observed away from the planet's bright aurorae,” said Dr Tom Stallard, Associate Professor in Planetary Astronomy and lead author of the study.
“The Great Cold Spot is much more volatile than the slowly changing Great Red Spot, changing dramatically in shape and size over only a few days and weeks, but it has re-appeared for as long as we have data to search for it, for over 15 years. That suggests that it continually reforms itself, and as a result it might be as old as the aurorae that form it - perhaps many thousands of years old.”
The astronomers revealed the presence of the Great Cold Spot as an area of darkness amongst the hot environment of Jupiter’s upper atmosphere by combining images taken over a period of time, including over 13,000 images taken over more than 40 nights by the InfraRed Telescope Facility.
“What is surprising at Jupiter is that, unlike weather systems on Earth, the Great Cold Spot has been observed at the same place across 15 years. That makes it more comparable to weather systems in Jupiter's lower atmosphere, like the Great Red Spot,” Dr Stallard, who is funded by the Science and Technology Facilities Council, added.
Dr Stallard said while the detection of the Great Cold Spot was a real surprise to them, there are indications that other features might also exist in Jupiter's upper atmosphere.
Their next step will be to look for other features in the upper atmosphere, while also investigating the Great Cold Spot itself in more detail, using ground telescopes as well as NASA's Juno spacecraft in orbit around Jupiter.
The new results have been published Tuesday in Geophysical Research Letters.