Jupiter’s Great Red Spot is a churning anticyclonic storm. It shows up in images of the giant planet as a conspicuous deep red eye embedded in swirling layers of pale yellow, orange and white. Winds inside this Jovian storm rage at immense speeds, reaching several hundreds of kilometres per hour.
Historic observations as far back as the late 1800s gauged this turbulent spot to span about 41 000 kilometres at its widest point — wide enough to fit three Earths comfortably side by side. In 1979 and 1980 the NASA Voyager fly-bys measured the spot at a shrunken 23 335 kilometres across. Now, Hubble has spied this feature to be smaller than ever before.
"Recent Hubble Space Telescope observations confirm that the spot is now just under 16 500 kilometres across, the smallest diameter we’ve ever measured," said Amy Simon of NASA’s Goddard Space Flight Center in Maryland, USA.
Amateur observations starting in 2012 revealed a noticeable increase in the spot’s shrinkage rate. The spot’s “waistline” is getting smaller by just under 1000 kilometres per year. The cause of this shrinkage is not yet known.
"In our new observations it is apparent that very small eddies are feeding into the storm," said Simon. "We hypothesised that these may be responsible for the accelerated change by altering the internal dynamics of the Great Red Spot."
Image credit: NASA, ESA, and A. Simon (GSFC); Acknowledgement: C. Go