In Summary

NASA has revealed that the Great Red Spot on Jupiter has shrunk to its smallest size ever and astronomers are unsure why.

The Great Red Spot is a giant anticyclone storm larger than Earth and has been raging for at least 400 years when astronomers were able to build telescopes large enough to see it, yet how it formed and has lasted this long is still a mystery.

Using the Hubble Space Telescope over the last two decades, astronomers were able to accurately measure the extent of the Great Red Spot, finding that it is shrinking by 1000km per year. The first observations in the 1800s measured the storm to be 41,000km across, wide enough to comfortably fit three Earths, but by 1979-80 it had shrunk to 23,335km.

Swinburne University of Technology astronomer Dr Alan Duffy says this iconic giant storm is still a mystery to astronomers after hundreds of years of effort, with even basic questions such as how it formed, how it has lasted so long and why it has the colour it does still unanswered.

“Few objects in the Solar System are as beautiful as this planet-sized raging anticyclone on Jupiter, yet for all the centuries of study we still have so many unanswered questions. On Earth we get anticyclones, which are regions of high pressure on a weather map, but they don’t last long as eventually they’ll pass over land and this drains the energy from the storm.

“As Jupiter is a gas giant it doesn’t have a land surface to slow down these storms and they can continue to build, although our current theories show the planet isn’t spinning fast enough to get a storm this large. However, we’ve seen smaller storms be engulfed by larger systems, and the Great Red Spot might just be a particularly successful storm in capturing neighbours to power itself to this size.

“With the precision of the Hubble Space Telescope we’ve recently seen the Great Red Spot swallow smaller ‘eddies’ or whirlwinds which might be somehow cancelling out the giant storm. This is a topic of intense research as we may only have a few years left to study it before it’s gone.

“With a width of 16,000km it’s still large enough to fit the Earth within the eye of the storm, yet at current rates it could be gone by 2030 which would be sad for the next generation of astronomers.

“When I give talks in schools the Great Red Spot is always a popular feature, and I’m often asked why it’s red. The incredible answer is that we don’t know for sure, although we think the colour is from complex organic molecules or sulphur-based compounds, we actually don’t know. Even more amazingly, the Great Red Spot can change colours from red to salmon pink to off-white, basically an interior decorator's dream,” Dr Duffy said.

“The clouds tower eight kilometers above their neighbours and the entire storm is spinning around at incredible speeds of hundreds of kilometers an hour, so would make for an impressive sight even though you could see a small part of this Earth-sized storm wall.”

Images and video of the research along with the press release can be found here.

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