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If anyone can explain why Jupiter's Great Red Spot is spinning faster and shrinking, please speak up
Astronomers are still figuring out how the planet's storm continues to rage
Video The winds whirring round the outer edge of Jupiter’s Great Red Spot have grown more powerful over the past decade, reaching speeds of at least 400 miles per hour, the Hubble Space Telescope has shown.
Astronomers have spent more than 150 years observing Jupiter’s iconic feature, a gigantic oval-shaped splodge measuring 10,000-plus miles across, which is wider than Earth. Flybys by NASA’s spacecraft Voyager and Juno revealed the Great Red Spot was made up of swirling red clouds driven by a ferocious storm.
The storm is still raging today, and scientists aren’t quite sure how. In fact, the outer winds have increased eight per cent in speed while the inner winds are slowing, according to measurements taken by Hubble from 2009 to 2020. The clouds are stirred into a frenzy, rotating counterclockwise around the center of the vortex.
“When I initially saw the results, I asked 'Does this make sense?' No one has ever seen this before," said Michael Wong, a researcher working at the University of California, Berkeley.
Wong tracked up to hundreds of thousands of wind vectors and analyzed their changes over a decade using software to figure out the increase in wind speed at the rim of the Great Red Spot. It turns out the wind is at least 400 miles per hour (180 metres per second).
“What does the increase in speed mean? "That's hard to diagnose, since Hubble can't see the bottom of the storm very well. Anything below the cloud tops is invisible in the data," Wong said. "But it's an interesting piece of data that can help us understand what's fueling the Great Red Spot and how it's maintaining energy."
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The gigantic oval vortex has changed since it was observed in the 1800s. Not only has the Great Red Spot started rotating faster, it has also decreased in size, and is becoming more circular over time.
“I do think these two changes are related, but it is difficult to prove or explain that,” Wong told The Register. “At this point, we are just publishing our new finding, and perhaps future simulation work will help us understand the changes.”
What’s powering these changes, however, remains a mystery as NASA’s latest video shows.
It’s difficult to study the Great Red Spot. There isn’t much data describing what’s going on inside the storm beyond the surface, and changes can often take a long time to notice.
For example, the changes in Hubble’s measurements of the Great Red Spot are relatively small; the wind speed changed at a rate of just 1.6 miles per hour per Earth year. The smallest detail astronomers can see on the Great Red Spot is 105 miles across, about twice the length of the US state of Rhode Island.
"We're talking about such a small change that if you didn’t have eleven years of Hubble data," said Amy Simon, a planetary scientist working at NASA's Goddard Space Flight Center.
“Since we don't have a storm chaser plane at Jupiter, we can't continuously measure the winds on site. Hubble is the only telescope that has the kind of temporal coverage and spatial resolution that can capture Jupiter’s winds in this detail."
Wong believes that studying the physics behind the Great Red Spot will help astronomers understand storms on other planets like Neptune and Saturn.
“Ultimately all these dynamical features are powered by heat: solar energy absorbed in the atmosphere heating it, and internal heat from deeper inside the planet. so we are studying the great red spot and other features to understand how the atmosphere is driven by this heat release,” he concluded. ®