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.
By analyzing images taken by NASA's Hubble Space Telescope from 2009 to 2020, researchers found that the average wind speed just within the boundaries of the Great Red Spot, set off by the outer green circle, have increased by up to 8 percent from 2009 to 2020 and exceed 400 miles per hour. In contrast, the winds near the storm's innermost region, set off by a smaller green ring, are moving significantly more slowly. Both move counterclockwise. Credits: NASA, ESA, Michael H. Wong (UC Berkeley)
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. "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.
The majority of the data to support this research came from Hubble's Outer
Planets Atmospheres Legacy program, which provides annual Hubble global
views of the outer planets that allow astronomers to look for changes in the
planets' storms, winds, and clouds.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.
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