The most famous and mysterious red dot in the history of humans and the planets that they can see so far just got a mysterious new neighbor. The Great Red Spot – discovered in the mid 1600s and confirmed by Voyager 2 to be an anticyclonic, high pressure storm twice the size of Earth – has been joined by the Great Cold Spot – a frigid area nearly as big as Big Red but not as reliable.
Tom Stallard, a planetary astronomer at the University of Leicester and lead author of a new study on the Great Cold Spot published in Geophysical Research Letters, says the spot was detected by astronomers using the Very Large Telescope in Chile and confirmed using 15 years worth of observations from another telescope. That data shows the Great Cold Spot being as stationary in Jupiter’s upper atmosphere as the Great Red Spot, but unlike Red it disappears occasionally, only to return eventually in the same location.
The causes of the Great Cold Spot are magnetic, meteorological, moon-related and mysterious, says Stallard. The 24,000 by 12,000 km (15,000 by 7,500 mile) spot is in Jupiter’s thin upper atmosphere, not a lower one like Great Red. It’s 200K (Kelvin) cooler than the upper atmosphere, which ranges between 700K (426ºC) and 1000K (726ºC).
Because Jupiter spins so fast, the spot is trapped above a pole rather than spreading around the planet like storms do on slow-spinning Earth. Being above the pole makes sense since the spot is the result of Jupiter’s aurora pushing heat energy into the upper atmosphere. Unlike the auroras on Earth and those newly discovered ones on Uranus (this must be Aurora Week), Jupiter’s are caused not by solar winds but by a steady stream of volcanic gases coming from the moon Io.
That explains the “what” of the Great Cold Spot, but what about the “why” … why is it cold?
The detection of a localized region of cooling within the upper atmosphere is unexpected. In the past, Jupiter's upper atmosphere was observed to have a gentle gradient of heat flowing away from the auroral region, and so the detection of such a localized cooling suggests that Jupiter's upper atmosphere is far more complex than previously thought.
In other words, it’s a mystery … and job security for astronomers studying Jupiter. The Great Cold Spot has most likely been there for thousands of years and keeps coming back after disappearing. Stallard says data from the Juno spacecraft currently orbiting Jupiter will be combined with past data and new observations to study the big new cold weather system.
Maybe they can spend a little of that time coming up with some better names for future spots.