Using Webb, scientists measure high-speed jet stream in Jupiter’s atmosphere

by Martijn Luinstra

Scientists recently discovered a high-speed jet stream at Jupiter’s equator using the joint NASA/European Space Agency/Canadian Space Agency James Webb Space Telescope. Webb’s images helped the team of scientists track fine details through the planet’s atmosphere, allowing them to measure these winds for the first time. The newly discovered jet stream will provide scientists with insight into how the layers of Jupiter’s turbulent atmosphere interact.

Webb observed the jet stream on July 27, 2022, when it peered into Jupiter’s lower stratosphere, the atmospheric layer above the planet’s cloud tops. The images allowed scientists to measure winds of up to 515 kilometers per hour, or about twice the sustained winds of a category five hurricane on Earth. The Jovian jet stream is located 40 kilometers above the clouds and, at approximately 4,800 kilometers wide, quite narrow relative to the immense size of Jupiter.

“This is something that totally surprised us,” said lead author Ricardo Hueso of the University of the Basque Country in Bilbao, Spain. “What we have always seen as blurred hazes in Jupiter’s atmosphere now appear as crisp features that we can track along with the planet’s fast rotation.”

Before Webb reached L2 and began performing scientific observations, scientists had been able to characterize the winds in the Jovian troposphere, the layer just below the stratosphere. Using ground-based telescopes and NASA’s Hubble Space Telescope, researchers were able to take infrared temperature measurements and resolve details in the clouds. Tracking how these clouds moved through the planet’s atmosphere allowed scientists to measure the winds at cloud level.

However, these previous observations did not reveal much detail in the haze above Jupiter’s clouds. These hazes showed up on images as featureless, low-contrast areas. But now, with Webb’s incredible suite of infrared instruments, scientists were finally able to receive detailed images of the entire planet across a broad spectrum of light, allowing them to discern and track faint details in the planet’s equatorial hazes for the first time.

Jupiter is a bright target for Webb, which meant the researchers had to limit the frequencies of light they observed. They did so by using filters on the telescope’s Near-Infrared Camera (NIRCam). These filters not only dimmed the planet enough for Webb to observe it but also allowed the researchers to target specific altitudes for their observations.

This diagram displays how Webb uses filters to observe various altitude ranges in the Jovian atmosphere. (Credit: NASA/ESA/CSA/STScI/R. Hueso (University of the Basque Country)/I. de Pater (University of California, Berkeley)/T. Fouchet (Observatory of Paris)/L. Fletcher (University of Leicester)/M. Wong (University of California, Berkeley)/J. DePasquale (STScI))

“It’s amazing to me that, after years of tracking Jupiter’s clouds and winds from numerous observatories, we still have more to learn about Jupiter, and features like this jet can remain hidden from view until these new NIRCam images were taken in 2022,” said co-author Leigh Fletcher of the University of Leicester in the United Kingdom.

Hueso et al. repeated their observations after the planet had completed one rotation, ten hours later. By doing this, the researchers could observe the same area twice and see how the atmosphere changed over time.

In order to wholly understand the dynamics of Jupiter’s atmosphere and the newly discovered jet stream, the scientists compared the images from Webb with observations Hubble had taken the day after. With Hubble’s images, they observed how the jet stream interacted with the cloud layer below it and measured how fast the winds changed with altitude and caused wind shears.

“We knew the different wavelengths of Webb and Hubble would reveal the three-dimensional structure of storm clouds, but we were also able to use the timing of the data to see how rapidly storms develop,” said co-author Michael Wong of the University of California, Berkeley, who led the associated Hubble observations.

Interestingly, scientists have long pondered the existence of this jet stream.

Ultraviolet (UV) images from NASA’s Cassini spacecraft gave scientists early hints of the now-confirmed jet stream. Cassini observed Jupiter in 2000 when it flew by on its way to its destination Saturn and showed an increase in wind speed a few kilometers above the clouds at Jupiter’s equator. Ultimately, Cassini’s measurements did not lead to firm conclusions, as the low contrast in the UV images caused large uncertainties in the measurements.

These highlights from Webb’s NIRCam images show how the details in Jupiter’s equatorial jet stream changed between one rotation of the planet (ten hours). (Credit: NASA/ESA/CSA/STScI/R. Hueso (University of the Basque Country)/I. de Pater (University of California, Berkeley)/T. Fouchet (Observatory of Paris)/L. Fletcher (University of Leicester)/M. Wong (University of California, Berkeley)/J. DePasquale (STScI))

Later in its mission, Cassini revealed equatorial jet streams on Saturn which are very similar to the newly discovered jets on Jupiter. By studying the differences and similarities between both planets, the researchers hope to unravel the mechanisms that shape the weather patterns around the equators of fast-rotating giant planets.

“Jupiter has a complicated but repeatable pattern of winds and temperatures in its equatorial stratosphere, high above the winds in the clouds and hazes measured at these wavelengths,” Fletcher explained. “If the strength of this new jet is connected to this oscillating stratospheric pattern, we might expect the jet to vary considerably over the next two to four years – it’ll be really exciting to test this theory in the years to come.”

The data used in this study was collected for Webb’s Early Release Science program. This program was set up to demonstrate the telescope’s full potential and explore its capabilities. This also allowed scientists to explore Webb data and plan follow-up observations.

“Even though various ground-based telescopes, spacecraft like NASA’s Juno and Cassini, and NASA’s Hubble Space Telescope have observed the Jovian system’s changing weather patterns, Webb has already provided new findings on Jupiter’s rings, satellites, and its atmosphere,” said Imke de Pater from the University of California. De Pater jointly led the Early Release Science program with Thierry Fouchet from the Observatory of Paris.

Hueso et al.’s results were published in Nature Astronomy on Oct. 19, 2023.

Lead image: False color image of Jupiter taken with Webb’s NIRCam. Credit: NASA/ESA/CSA/STScI/R. Hueso (University of the Basque Country)/I. de Pater (University of California, Berkeley)/T. Fouchet (Observatory of Paris)/L. Fletcher (University of Leicester)/M. Wong (University of California, Berkeley)/J. DePasquale (STScI)

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