The Hubble Space Telescope has recorded higher wind speeds in the famous Jovian storms in recent years.
By Isaac Schultz
Jupiter as seen on August 25, 2020. Image: NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team
NASA’s Hubble Space Telescope keeps an eye on Jupiter’s Great Red Spot, a 10,000-mile-wide storm system that has been swirling for at least 190 years and possibly much longer. Recent data from the telescope indicates that the spot’s outer winds have picked up speed in the past decade.
The storm has an “outer lane” and an “inner lane” of winds, both of which rotate counterclockwise. While the outer lane has sped up recently, the winds closer to the center of the spot were actually moving much slower in 2020 than they were back in 2009. The research exploring these wind trends was published last month in the Astrophysical Journal Letters.
“Since we don’t have a storm chaser plane at Jupiter, we can’t continuously measure the winds on site,” said Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center, in a NASA press release. “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 pickup in wind speed was steady: less than a 2-mile-per-hour change per Earth year from 2009 to 2020. It’s only because the team had 11 years of Hubble data, and that Hubble can see Jupiter with such precision, that they could pick out the trend. The winds are blowing at around 400 miles per hour, slightly slower than the cruising speed of a commercial airliner.
The counterclockwise winds of Jupiter’s Great Red Spot, shown in visible light (left) and in a velocity map (right). Image: NASA, ESA, Michael H. Wong (UC Berkeley)
“Hubble can’t see the bottom of the storm very well. Anything below the cloud tops is invisible in the data,” said Michael Wong, a planetary scientist specializing in atmospheres at the University of California at Berkeley, and the paper’s lead author, in the same release. Wong added that the recent trend is “an interesting piece of data that can help us understand what’s fueling the Great Red Spot and how it’s maintaining energy.”
The Great Red Spot, as imaged by Voyager 1 in 1979.Image: NASA
Planetary scientists do know some things about the spot. It has a tiered structure in which the storm’s higher clouds are toward the center, and the outer edges of the storm are deeper in the planet. The storm is slowly becoming more circular compared to the oval it’s long been.
The storm has been observed for nearly 200 years—maybe even 350 years, as it’s hard to say whether spots described by earlier astronomers were one and the same as the Great Red Spot—but it’ll likely take more time and better instruments to dig deeper into the tempestuous mystery at Jupiter’s heart.
More: Jupiter’s Great Red Spot Is About to Reveal Its Mysteries
Hubble shows winds in Jupiter's great red spot are speeding up
Like the speed of an advancing race car driver, the winds in the outermost "lane" of Jupiter's Great Red Spot are accelerating – a discovery only made possible by NASA's Hubble Space Telescope, which has monitored the planet for more than a decade.
Researchers analyzing Hubble's regular "storm reports" found that the average wind speed just within the boundaries of the storm, known as a high-speed ring, has increased by up to 8 percent from 2009 to 2020. In contrast, the winds near the red spot's innermost region are moving significantly more slowly, like someone cruising lazily on a sunny Sunday afternoon.
The massive storm's crimson-colored clouds spin counterclockwise at speeds that exceed 400 miles per hour – and the vortex is bigger than Earth itself. The red spot is legendary in part because humans have observed it for more than 150 years.
"When I initially saw the results, I asked 'Does this make sense?' No one has ever seen this before," said Michael Wong of the University of California, Berkeley, who led the analysis published today in Geophysical Research Letters. "But this is something only Hubble can do. Hubble's longevity and ongoing observations make this revelation possible."
We use Earth-orbiting satellites and airplanes to track major storms on Earth closely in real time. "Since we don't have a storm chaser plane at Jupiter, we can't continuously measure the winds on site," explained Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who contributed to the research. "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 change in wind speeds they have measured with Hubble amount to less than 1.6 miles per hour per Earth year. "We're talking about such a small change that if you didn't have eleven years of Hubble data, we wouldn't know it happened," said Simon. "With Hubble we have the precision we need to spot a trend." Hubble's ongoing monitoring allows researchers to revisit and analyze its data very precisely as they keep adding to it. The smallest features Hubble can reveal in the storm are a mere 105 miles across, about twice the length of the state of Rhode Island.
"We find that the average wind speed in the Great Red Spot has been slightly increasing over the past decade," Wong added. "We have one example where our analysis of the two-dimensional wind map found abrupt changes in 2017 when there was a major convective storm nearby."
To better analyze Hubble's bounty of data, Wong took a new approach to his data analysis. He used software to track tens to hundreds of thousands of wind vectors (directions and speeds) each time Jupiter was observed by Hubble. "It gave me a much more consistent set of velocity measurements," Wong explained. "I also ran a battery of statistical tests to confirm if it was justified to call this an increase in wind speed. It is."
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," explained Wong. "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." There's still a lot of work to do to fully understand it.
Astronomers have pursued ongoing studies of the "king" of solar system storms since the 1870s. The Great Red Spot is an upwelling of material from Jupiter's interior. If seen from the side, the storm would have a tiered wedding cake structure with high clouds at the center cascading down to its outer layers. Astronomers have noted that it is shrinking in size and becoming more circular than oval in observations spanning more than a century. The current diameter is 10,000 miles across, meaning that Earth could still fit inside it.
In addition to observing this legendary, long-lived storm, researchers have observed storms on other planets, including Neptune, where they tend to travel across the planet's surface and disappear over only a few years. Research like this helps scientists not only learn about the individual planets, but also draw conclusions about the underlying physics that drive and maintain planets' storms.
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