Hubble Measures Horizontal Winds in Jupiter’s Great Red Spot

Using data from the WFC3/UVIS instrument on board the NASA/ESA Hubble Space Telescope, a team of astronomers has measured the horizontal winds in Jupiter’s most distinctive feature, the Great Red Spot. By analyzing the long-term data from the boundaries of the giant storm, known as the high-speed ring, they’ve found that the wind speed has increased by up to 8% between 2009 and 2020; in contrast, the winds near the storm’s innermost region are moving significantly more slowly.

The Great Red Spot is an enduring large anticyclone in the atmosphere of Jupiter. It is like a hurricane on Earth, but it is much larger.

The storm’s colored clouds spin counterclockwise at speeds that exceed 640 km per hour (398 mph).

Nobody knows when the Great Red Spot first appeared on Jupiter, but it has been seen on the planet ever since people started looking through telescopes about four centuries ago.

“When I initially saw the results, I asked ‘Does this make sense?’ No one has ever seen this before,” said Dr. Michael Wong, an astronomer in the Center for Integrative Planetary Science at the University of California, Berkeley.

“But this is something only Hubble can do. Hubble’s longevity and ongoing observations make this revelation possible.”

In the study, Dr. Wong and colleagues analyzed data gathered by Hubble between 2009 and 2020.

“Since we don’t have a storm chaser plane at Jupiter, we can’t continuously measure the winds on site,” said Dr. Amy Simon, an astronomer at NASA’s Goddard Space Flight Center.

“Hubble is the only telescope that has the kind of temporal coverage and spatial resolution that can capture Jupiter’s winds in this much detail.”

The change in wind speed the researchers have measured with Hubble amounts to less than 2.5 km per hour (1.6 mph) per Earth year.

“We’re talking about such a small change that if we didn’t have eleven years of Hubble data, we wouldn’t know it had happened,” Dr. Simon said.

“With Hubble we have the precision we need to spot a trend.”

“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,” Dr. Wong said.

“But it’s an interesting piece of the puzzle that can help us understand what’s fueling the Great Red Spot and how it’s maintaining its energy.”

“There’s still a lot of work to do to fully understand it.”

Some changes in the Great Red Spot wind patterns happened at the same time as a giant nearby storm in 2016 and 2017, but the scientists did not find changes at the same time as ‘flaking’ events in 2019.

“By ‘flaking’ we mean pictures showing that small areas of red, normally kept inside the giant storm, detached and blew away from it,” they said.

The findings were published in the Geophysical Research Letters.

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Michael H. Wong et al. 2021. Evolution of the Horizontal Winds in Jupiter’s Great Red Spot From One Jovian Year of HST/WFC3 Maps. Geophysical Research Letters 48 (18); doi: 10.1029/2021GL093982

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