The images on the left show the bright arcs of Jupiter’s infrared aurora on two separate nights, the top left image on 17 October and three images taken 31 December 2012, as the planet slowly rotates. However, the Great Cold Spot cannot be seen clearly until these images are saturated so that the entire aurora becomes white, as shown on the right. Here, the planet glows as a result of the temperature of the upper atmosphere, and the distinct regions of cooling that reveal the Great Cold Spot can be seen. Based on data from VLT/ESO

Astronomers from the University of Leicester announced the discovery of a second “Great Spot” located in Jupiter’s upper atmosphere.

The “Great Cold Spot” is almost as large as its famous sibling, the “Great Red Spot” – measuring 24,000 km (14,912 miles) in longitude and 12,00 km (7,456 miles) in latitude.

The weather feature has likely existed for thousands of years, but previous observations of the planet have been limited by spatial resolution.

“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 aurora that form it - perhaps many thousands of years old,” said Tom Stallard, associate professor in planetary astronomy and lead author of the study.

Stallard and fellow researchers believe the effects of Jupiter’s magnetic field caused the Great Cold Spot, with the polar aurora transporting energy into the atmosphere in the form of heat flowing around the planet. Some type of interaction appears to form a vortex, resulting in a localized region of cooling in the thermosphere.

The researchers claim this is the first time any weather feature in Jupiter’s upper atmosphere has been observed away from the planet’s bright aurora.

“The feature we’re seeing is away from the aurora, which is what makes it so unusual,” said Stallard in a university video.

The finding provides evidence that Jupiter’s upper atmosphere is much more complex than previously thought. The CRIRES instrument on the Very Large Telescope (VLT) spotted the phenomenon.

Study results were published today in Geophysical Research Letters.

The next step is to determine if this feature is truly unique to Jupiter’s upper atmosphere, or if similar features are actually common.