The images show the aurora above Jupiter's pole. On the right the images have been saturated to allow the Great Cold Spot to become visible. Credit: VLT/ESO
New images from the Very Large Telescope have revealed a colossal Great Cold Spot on Jupiter, a cool patch in the planet’s polar atmosphere that appears to be created by aurora.
The Cold Spot is 24,000km long and 12,000km wide, a size that rivals its better-known twin, the Great Red Spot.
It is located in the Gas Giant’s thin high-altitude thermosphere, but is around 200K cooler than the surrounding atmosphere, which ranges in temperature from 700K to 1,000K.
“The Great Cold Spot is much more volatile than the slowly changing Great Red Spot," says Tom Stallard, an associate professor in planetary astronomy from theUniversity of Leicesterand lead author on the project.
[The Great Cold Spot] changes 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.”
It’s thought that the cold spot is caused by Jupiter’s aurora driving energy into the atmosphere in the form of heat that flows across the planet.
This creates a region of cooling in the boundary layer between the underlying atmosphere and the vacuum of space – the thermosphere.
Though the precise nature of this weather feature is unknown it’s thought to be similar to the vortex driven by the Great Red Spot.
The spot was found using the Very Large Telescope, which mapped the temperature profile of the planet’s atmosphere.
This was then compared to images taken by NASA’s InfraRed Telescope Facility between 1995-2000.
“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,” says Stallard.
“The Juno spacecraft is currently in orbit around Jupiter and the observations of Jupiter’s aurora and upper atmosphere by the JIRAM instrument that have been released so far already provide a wealth of new information about the planet,” Stallard continues.
“When combined with our ongoing campaign of observations using telescopes on Earth, we hope to gain a much better understanding of this weather system in the next few years.”