Jupiter’s Red Spot Shrinks To Smallest Size Ever – How Long Will It Last?

In this comparison image the photo at the top was taken by the Hubble Space Telescope in 1995 and shows the spot at a diameter of just under 13,050 miles (21,000 km); the second down shows a 2009 photo of the spot at a diameter of just under 11,180 miles (18,000 km); and the lowest shows the newest image from taken in 2014 with the spot at its smallest yet, with diameter of just 9,940 miles (16,000 km). Credit: NASA/ESA

The Great Red Spot is arguably Jupiter’s most iconic feature. Mention the giant planet and most of us conjure up an image of striped gas ball with a big red beauty mark.

While the spot has been observed since the infancy of the telescope, we’ve come to accept it as a permanent part of the Jovian planet’s persona. Now it’s time to admit the truth. The Great Red Spot has been downsizing since the 1930s with particularly swift changes happening in just the last couple decades.

Ask any long-time amateur astronomer. Back in the 1960s the spot extended over a greater area and was more elongated or stretched out. In the past few years, its not only contracted thousands of miles but become more circular. Most of us have blamed the spot’s pale, watered-down color in recent years as the reason it’s become more difficult to see.

At left, photo of Jupiter’s enormous Great Red Spot in 1879 from Agnes Clerk’s Book ” A History of Astronomy in the 19th Century”. At right, Jupiter on Jan. 10, 2014. Credit: Damian Peach

But that’s only part of the problem. Since 1995 it’s downsized by over 3,000 miles. That’s nearly half an Earth diameter in 20 years! Since 2012 it’s been losing girth at the rate of 580 miles a year. 130 years ago the spot spanned about 25,000 miles (40,000 km) and looked like a giant blimp riding Jupiter’s cloud belts. Even in the small 2-3 inch refracting telescopes popular at the time it would have hard to miss. Now you need at least a 6-inch telescope to see it clearly.

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

Reprocessed view by Bjorn Jonsson of the Great Red Spot made by Voyager 1 in 1979 reveals an incredible wealth of detail. The Spot is a vast, long-lived. hurricane-like storm located between opposing jet streams in Jupiter’s southern hemisphere. Click to enlarge. Credit: NASA

The not-so Great Red Spot (GRS) is a hurricane-like storm that rotates anticlockwise in Jupiter’s southern hemisphere immediately south of the prominent South Equatorial Belt. It takes its swirly appearance from winds blowing at several hundred miles an hour with the spot’s cloudtops reaching 5 miles (8 km) above Jupiter’s cloud deck.

Animation showing the rotation of the Great Red Spot made with images taken by NASA’s Voyager 1 spacecraft . Credit: NASA

The spot used to rotate once every 6 days, but smaller eddies or vortices feeding into the spot that may be responsible for its changing appearance have shortened that to about 4 days.

Red Spot Jr. on Feb. 1, 2014. It’s the first significant new red spot ever observed on Jupiter and located at longitude 332 degrees (Sys. II) The spot about half the width of the more familiar Great Red Spot. Credit: Christopher Go

What will become of the spot is anyone’s guess. It may continue to wither and disappear altogether. It is does go bye-bye, Red Spot Jr. waits in the wings. This new but considerably smaller red-tinted spot formed from the merger of three smaller oval vortices between 1998 and 2000. Or we could be completely surprised and see it revivified by the Jovian jet streams. Such is weather, whether here or on Jupiter, there will always be an element of unpredictability.

NASA’s Juno spacecraft is hurtling toward Jupiter now, due to reach the giant planet in July 2016.  Up close examination by the probe will hopefully fill in holes in our knowledge of the planet’s turbulent and fascinating atmosphere.

5 Responses

  1. Troy

    Since the GRS continues to exist by consuming other storms, and Red Jr. isn’t that far away (in latitude), I wonder if Red Jr. is growing at the expense of GRS?
    I’ve always wondered why there isn’t a corresponding spot in the northern hemisphere.

    1. astrobob

      I’ve always wondered the same, though there have been many mid-northern latitude vortices (smaller storms). Red Spot Jr. swept past the Red Spot sometime in the past few years. Who knows – it may have had a small effect.

      1. caralex

        Can you imagine the weather for the poor Jovians who’ve had to live under that spot for hundreds of years?! :p

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