In a First, Juno Probe Will Fly Over the Great Red Spot of Jupiter

Jupiter’s defining feature is the Great Red Spot, a swirling vortex of gas about 10,250 miles (10,250) kilometers in diameter. We don’t know how long this giant storm has been active, but it may have been observed as early as 1664 by Robert Hooke. All these years later, we’re about to get our first up-close look at the Great Red Spot thanks to the Juno probe. It’s a good thing, too—the Great Red Spot is shrinking fast, and we don’t know why.

The Juno probe arrived in Orbit of Jupiter just over a year ago, and has since maneuvered itself into an eccentric 53-day orbit of the planet. It was originally supposed to shorten its orbital period to 20 days, but issues with helium valves essential to the main engines caused NASA to err on the side of caution. Juno has already sent back several rounds of data from Jupiter, but the next one will be particularly fascinating. This evening (July 10th), Juno will pass directly over the Great Red Spot.

At 6:55 PM PDT today, Juno will reach its lowest altitude over Jupiter, just 2,200 miles (3,500 kilometers) above the cloud tops. Eleven minutes and 33 seconds later, Juno will be directly above the Great Red Spot, which itself protrudes above the rest of the clouds. Juno’s altitude will have increased by this point in its flyby, but it will still be a mere 5,600 miles (9,000 kilometers) above the Red Spot. This is considerably closer than Voyager 1 got when it flew past Jupiter on its way out of the solar system in 1979.

Jupiter’s Great Red Spot, taken by Voyager 1.

Juno is equipped with instruments designed to peer through the cloud layers and gather data on the inner workings of Jupiter’s atmosphere. This could allow scientists to better understand what drives this massive storm, which has persisted for centuries. Although, it’s been shrinking rapidly in recent decades. In the late 1800s it was more than 25,000 miles in diameter, but now it’s just 10,250 miles across at its widest point. Astronomers calculate the storm is shrinking by nearly 600 miles per year. No one knows if the Great Red Spot will continue fading away or if it’ll ramp back up. Juno’s observations might help us figure that out.

NASA will use instruments like the microwave radiometer and gravity science module to gather important data about the Great Red Spot and underlying structures, but there will also be some pretty pictures captured with the JunoCam. Some of the images sent back from Juno’s previous passes have been awe-inspiring, and these images could be the best yet. In the coming days, NASA should release between 10 and 100 images from this flyby, depending on the level of compression used.

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