Wind speed increases to 300 mph in Jupiter’s Great Spot as its radius decreases

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Jupiter’s Great Red Spot is as constant as the North Star. In other words, it only looks constant — its constancy depends on how long we watch it. …

Three shots by amateur astronomers taken on September 7th (top) and 8th (bottom), in which a small blemish (marked by the orange triangle) circles the Great Red Spot. Using these and other amateur images, Rogers was able to clock the storm's rotation period. / J.H. Rogers, D. Peach, G. Walker, and D. Parker

Last week John Rogers (British Astronomical Association) confirmed that the storm is still tightening its waistline. Rogers clocked the maelstrom’s rotation period by using images taken by an international network of amateur astronomers. These images followed a dark streak as it whipped three times around the spot, providing a marker to gauge how fast the storm clouds whirligig. The circulating blemish made the trek in 4.0 days, shorter than the 4.5 days Rogers measured in 2006 using the same method.

The GRS’s outer radius hasn’t shrunk much since 2006 (it’s a bit less than 20,000 km wide now). …

Rogers also estimated a max wind speed of 135 m/s (300 mph), up from about 112 m/s in 2006. That’s consistent with the range of 118-132 m/s measured directly by Hubble in 2006, and the vortex’s rotation speed has generally fluctuated within this range without any overall trend. Still, Glenn Orton (Jet Propulsion Laboratory) suggests that the speed uptick between 2006 and 2012 might be an overall change related to the vortex’s shrinkage. It could be that, somewhat like an ice skater spinning faster as she pulls in her arms, the storm’s rotation speed is rising as it shrinks.

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