Jupiter’s massive Great Red Spot is at least 350 kilometers deep

NASA’s Juno spacecraft has measured the storm’s depth for the first time


HIDDEN DEPTHS  Jupiter’s Great Red Spot (left in this image from NASA’s Juno spacecraft) extends down into the planet’s atmosphere at least 350 kilometers, as far as Juno can see.

Seán Doran, Gerald Eichstädt, MSSS, SwRI, JPL-Caltech/NASA 

NEW ORLEANS — Jupiter’s Great Red Spot has deep roots. Data from the first pass of NASA’s Juno spacecraft over the incessant storm show that its clouds stretch at least 350 kilometers down into the planet’s atmosphere. That means the storm is about as deep as the International Space Station is high above the Earth.

Juno has been orbiting Jupiter since July 4, 2016, and it made its first close flyby of the red spot about a year later (SN Online: 7/7/17). As the spacecraft swooped 9,000 kilometers above the giant storm, Juno’s microwave radiometer peered through the deep layers of cloud, measuring the atmosphere’s temperature down hundreds of kilometers.

“Juno is probing beneath these clouds, and finding the roots of the red spot,” Juno co-investigator Andrew Ingersoll of Caltech said December 11 at a news conference at the American Geophysical Union’s fall meeting. Cheng Li of Caltech presented the research at AGU on December 12.

<b>ROUND AND ROUND</b> This animation, based on images from NASA’s Juno spacecraft, simulates the motion in Jupiter’s Great Red Spot.</b> NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Justin Cowart
The radiometer probes different layers of the atmosphere by measuring the gas in six different microwave wavelengths. Ingersoll and his colleagues found that the gas beneath the red spot’s surface gets warmer with depth, and a warm zone at the same location as the spot was visible down to 350 kilometers .

The fact that the 16,000-kilometer-wide spot is warmer at the bottom than at the top could help explain the storm’s screaming wind speeds of about 120 meters per second. Warm air rises, so the internal heat could provide energy to churn the storm.

Juno principal investigator Scott Bolton of the Southwest Research Institute in San Antonio notes that the spot “goes as deep as we can see,” but it could go deeper.  “I’m not sure we’ve established the true foot,” he says.  On a future flyby, Juno will try to use gravity data to detect the storm at depths of thousands of kilometers. If the spot does go down that deep, theorists will struggle to explain why, Bolton says.

The only previous data on Jupiter’s interior came from the Galileo spacecraft, which ended its mission by entering Jupiter’s atmosphere at a single point in 1995. “I like to say that if aliens sent a probe to Earth and it landed in the Sahara, they would conclude the Earth is all desert,” says planetary scientist Michael Wong of Caltech, who was not involved in the new study. “Juno getting this global view gives us a new understanding of the inner workings … We have never really seen the interior of a giant planet in this way before.” 

Lisa Grossman is the astronomy writer. She has a degree in astronomy from Cornell University and a graduate certificate in science writing from University of California, Santa Cruz. She lives near Boston.

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