The shrinkage of Jupiter's Great Red Spot has been known about since the 1930s but latest images by Hubble Space Telescope confirm the increasing shrinkage rate observed by amateur astronomers since 2012. Science has no answer as to why this is happening.
Historic observations as far back as the late 1800s estimated this turbulent spot to span about 41 000 kilometers at its widest point. In 1979 and 1980 the NASA Voyager fly-bys measured the spot at a shrunken 23 335 kilometers across.
Hubble Space Telescope observations from April 2014 showed that the spot is now just under 16 500 kilometers across, the smallest diameter ever measured.
In this comparison image the photo at the top was taken by Hubble's Wide Field Planetary Camera 2 in 1995 and shows the spot at a diameter of just under 21 000 km; the second down shows a 2009 WFC3 photo of the spot at a diameter of just under 18 000 km; and the lowest shows the newest image from WFC3 taken in 2014 with the spot at its smallest yet, with diameter of just 16 000 km. Image credit: NASA, ESA, and A. Simon (Goddard Space Flight Center).
The Great Red Spot is a high-pressure anticyclone. It rotates in an anti-clockwise direction in Jupiter's southern hemisphere and 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 kilometers per hour.
"In our new observations it is apparent that very small eddies are feeding into the storm," said Amy Simon of NASA's Goddard Space Flight Center. "We hypothesized that these may be responsible for the accelerated change by altering the internal dynamics of the Great Red Spot."
Simon's team plan to study the motions of these eddies, and also the internal dynamics of the spot, to determine how the stormy vortex is fed with or sapped of momentum.
Source: Hubble Space Telescope
Featured image: NASA, ESA, and A. Simon (Goddard Space Flight Center).