Jupiter's Great Red Spot is getting smaller

NASA announced that measurements of Jupiter's Great Red Spot taken from the Hubble Space Telescope (HST) confirm that the swirling anti-cyclonic storm is at its smallest ever, 10,250 miles wide.

Posted 11:32 p.m. May 15, 2014 — Updated 11:34 p.m. May 15, 2014

Tony Rice

NASA announced that measurements of Jupiter’s Great Red Spot taken from the Hubble Space Telescope (HST) confirm that the swirling anti-cyclonic storm is at its smallest ever, 10,250 miles wide. German astronomer Samuel Heinrich Schwabe first noted the spot in the early 1800s.

Voyager 1 and Voyager 2 fly-bys of Jupiter in 1979 measured it to be 14,500 miles across. The Hubble telescope estimated it at 13,020 miles across in 1995 and 11,130 miles across in 2009. Changes in the spot have been tracked since the 1930s but have accelerated in recent years.

Amateur astronomers noted significant increases in the spot's width in 2012. It changed from an oval to nearly circular. Scientists are not sure what is causing these changes but have noted changes in circulation around the storm.

"In our new observations, it is apparent very small eddies are feeding into the storm," explained Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Md. "We hypothesized these may be responsible for the accelerated change by altering the internal dynamics and energy of the Great Red Spot."

Scientists think the spot's reddish color comes from sulfur and phosphorus possibly created by lighting in the upper reaches of the storm extending 5 miles above the neighboring clouds. Jupiter has the shortest day in the solar system with a rotational frequency more than double Earth's causing the planet to bulge at the equator.

The Great Red Spot faces Earth several times each day and is visible with moderate-sized telescopes. It will next be visible Saturday evening from about 8:30 p.m. to about 10:30 p.m. It will be visible again during Morehead Planetarium's free Skywatching event May 31 from 9 p.m. to 11 p.m. at Jordan Lake.

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