Lauren Fuge
Editor, Cosmos Magazine
The Great Red Spot on Jupiter is a vast storm that has been raging for at least 150 years, and new analysis shows that its winds are changing.
The storm is an anticyclone big enough to swallow our entire planet, with massive, crimson-coloured clouds spinning in an anticlockwise direction. The winds raging on the outer edge are more than twice as intense as a Category 5 cyclone on Earth, while the winds within the storm are cruising around more slowly.
Now, a new study published in the Journal of Geophysical Research has found that the outer winds have sped up.
Using data from the Hubble Space Telescope from 2009 to 2020, the research team found that mean wind speeds in the Great Red Spot have increased by 4% to 8%.
This correlates to winds increasing in speed by only 2.5km/h every (Earth) year, so they now blow at more than 640km/h.
“When I initially saw the results, I asked, ‘Does this make sense?’ says Michael Wong, lead author of the study from the University of California, Berkeley in the US. “No one has ever seen this before.”
Co-author Amy Simon, from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, explains that Hubble made the revelations possible.
“We’re talking about such a small change that if you didn’t have 11 years of Hubble data, we wouldn’t know it happened,” she says. “Hubble is the only telescope that has the kind of temporal coverage and spatial resolution that can capture Jupiter’s winds in this detail.”
The team used software to track hundreds of thousands of wind vectors (measurements taking into account both direction and speed) to observe the change over time.
But what does this speed increase mean?
“That’s hard to diagnose, since Hubble can’t see the bottom of the storm very well,” says Wong. “Anything below the cloud tops is invisible in the data. 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.”
The storm is also changing shape, becoming less cigar-shaped and more circular.
Previous research has additionally shown that the Great Red Spot is shrinking, but we still don’t know much about when and how it formed, why it has such a striking red colour, or why it is so long-lived.
Data from NASA’s Juno spacecraft, which is currently in orbit around Jupiter, may help shed further light on this monstrous storm.