‘Textbooks need to be updated’: Juno spacecraft reveals Jupiter is smaller and flatter than we thought

Jupiter is slightly smaller and flatter than scientists thought for decades, a new study has found.

Researchers used radio data from the Juno spacecraft to refine measurements of the solar system’s largest planet. Although the differences between the current measurements and previous measurements are small, models of Jupiter’s interior and other gas giants like Jupiter outside our solar system have improved, the researchers reported in the journal Nature Astronomy on February 2.

“Textbooks need to be updated,” study co-author Yohai Caspi, a planetary scientist at the Weizmann Institute of Science in Israel, said in a statement. “Of course, Jupiter’s size hasn’t changed, but the way we measure Jupiter has changed.”

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Until now, scientists’ understanding of Jupiter’s size and shape was based on six measurements made by the Voyager 1 and 2 and Pioneer 10 and 11 missions. These measurements, which have since been adopted as a standard, were carried out using radio beams about 50 years ago, according to the statement.

But the Juno mission has been collecting data on Jupiter and its moons since arriving at the gas giant in 2016, and has collected even more radio data over the past two years. With that additional data, researchers have now refined measurements of Jupiter’s size to about 1,300 feet (400 meters) in each direction.

“You can figure out Jupiter’s size and shape just by knowing its distance and observing how it rotates,” Caspi said. “But to make really accurate measurements, we need more sophisticated methods.”

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In the new study, scientists tracked how the radio signal returning to Earth from Juno curves as it passes through Jupiter’s atmosphere and is cut off when Jupiter blocks the signal completely. These measurements allowed the team to explain Jupiter’s winds, which slightly change the shape of the gas planet. They then used that information to accurately calculate the shape and size of the planet.

Using the new data, the research team calculated that the radius of the planet from pole to center is 41,534 miles (66,842 km). This is 7.5 miles (12 km) smaller than previous measurements. The newly calculated radius at the equator is 44,421 miles (71,488 km), 2.5 miles (4 km) smaller than previously thought.

“These few kilometers are important,” study co-author Eli Galanti, an expert on gas giant planets at the Weizmann Institute of Science, said in a statement. “By shifting the radius by a small amount, Jupiter’s interior model fits both the gravity data and atmospheric measurements much better.”

The updated measurements will improve our understanding of Jupiter’s interior and help scientists interpret data from gas giants outside our solar system, the researchers wrote in a study.

“This research helps us understand how planets form and evolve,” Caspi said in a statement. “Jupiter was probably the first planet to form in our solar system, and studying what happens inside it brings us closer to understanding how our solar system and planets like us formed.”