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First look at weather inside Jupiter's red spot
Posted: 17 March 2010

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Stunning new thermal images derived from ground-based telescopes reveal the first detailed weather maps of Jupiter's giant storm system.

Observations of the Great Red Spot date back for hundreds of years; it is the longest persisting – and largest – storm in the Solar System, capable of consuming Earth two to three times over. It churns around in an anticlockwise direction with a period of about six Earth days.

Jupiter's Great Red Spot as never seen before. The top image was obtained with the VLT in the infrared wavelength range of 10.8 microns, which is sensitive to Jupiter's atmospheric temperatures in the 300 to 600 millibar pressure range. That pressure range is close to the altitude of the white, red and brown aerosols seen in the visible-light image (bottom), which was obtained by the Hubble Space Telescope. Image: ESO/NASA/JPL/ESA/L. Fletcher.

The new images, derived from the VISIR instrument (VLT Imager and Spectrometer for mid Infrared) on ESO's Very Large Telescope (VLT), the Gemini South telescope and the National Astronomical Observatory of Japan's Subaru Telescope, show swirls of warmer air and cooler regions never seen before within the red spot. The images have enabled scientists to link the spot's temperature, winds, pressure and composition to its colour. Impressively, by combining the thermal data with observations of the deep cloud structure by the three-metre NASA Infrared Telescope Facility in Hawaii, the level of detail is comparable to visible light images from the space-based Hubble Space Telescope.

“This is the first time we can say that there’s an intimate link between environmental conditions – temperature, winds, pressure and composition – and the actual colour of the Great Red Spot,” says lead author of the study Leigh Fletcher. “Although we can speculate, we still don’t know for sure which chemicals or processes are causing that deep red colour, but we do know now that it is related to changes in the environmental conditions right in the heart of the storm.”

The reddest colour of the spot corresponds to a warm core within the otherwise cold storm system that averages -160 degrees Celsius, with dark lanes at the edge of the storm marking the locations where gases are sinking deeper into the planet.

“One of the most intriguing findings shows the most intense orange-red central part of the spot is about three to four degrees warmer than the environment around it,” adds Fletcher. This temperature difference is enough to cause a weak clockwise rotation in the very centre of the storm, opposite to the dominant anti-clockwise motion the rest of the storm undergoes.

The VISIR measurements also allow scientists to map the temperature, aerosols and ammonia within and surrounding the storm, which provides further information on how the weather and circulation patterns change within the storm, in three dimensions and over time. Looking at measurements taken over several years shows that the storm is surprisingly stable considering it undergoes turbulence, upheavals and close encounters with other anticyclones, such as the so-called 'baby red spot' or 'red spot junior'.

“This is our first detailed look inside the biggest storm of the Solar System,” says Glenn Orton, who led the team of astronomers that made the study. “We once thought the Great Red Spot was a plain old oval without much structure, but these new results show that it is, in fact, extremely complicated.”

The research will be published in a forthcoming issue of the journal Icarus.