Jupiter’s Great Red Spot is Shrinking

The Great Red Spot on Jupiter is shrinking, says a team of astronomers led by Dr Amy Simon of NASA’s Goddard Space Flight Center in Maryland.

This full-disc image of Jupiter was taken on 21 April 2014 with Hubble’s Wide Field Camera 3. Image credit: NASA / ESA / A. Simon, Goddard Space Flight Center.

Jupiter’s Great Red Spot is a high-pressure anticyclone. This monster storm shows up in images as a conspicuous deep red eye embedded in swirling layers of pale yellow, orange and white. It rotates in an anti-clockwise direction in the planet’s southern hemisphere. Winds inside it rage at immense speeds, reaching several hundreds of km per hour.

The Great Red Spot itself may have been mentioned in writings before the late 1800s. There are references to Jupiter’s ‘permanent spot’ dating back as far as the late 1600s, although some astronomers disagree that the permanent spot mentioned is the Great Red Spot.

Historic observations gauged this turbulent spot to span about 41,000 km at its widest point – wide enough to fit three Earths comfortably side by side.

In 1979 and 1980, NASA’s Voyager fly-bys measured the Great Red Spot at a shrunken 23,335 km across.

In this comparison image the photo at the top was taken by Hubble in 1995 and shows the spot at a diameter of just under 21,000km; the second shows a 2009 photo of the spot at a diameter of just under 18,000 km; and the lowest shows the newest image from Hubble taken in 2014 with the spot at its smallest yet, with diameter of just 16,000 km. Image credit: NASA / ESA / Z. Levay, STScI.

Now, new images from NASA’s Hubble Space Telescope capture the spot at a smaller size than ever before.

Dr Simon said: “recent Hubble observations confirm that the spot is now just under 16,500 km across, the smallest diameter we’ve ever measured,”

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 1,000 km 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. We hypothesized that these may be responsible for the accelerated change by altering the internal dynamics of the Great Red Spot,” Dr Simon said.