After 50 years, scientists found that Jupiter is smaller and flatter than expected, NASA’s Juno reveals

uno’s Precision Measurements Show Jupiter Isn’t Quite the Planet Scientists Thought It Was (Image: Canva)

Scientists using radio data from NASA’s Juno spacecraft have refined Jupiter’s size and shape, finding it slightly smaller and flatter than measurements made decades ago. Published in Nature Astronomy, the study improves understanding of Jupiter’s interior and atmospheric dynamics. By tracking how radio signals bent through the planet’s atmosphere, researchers achieved far more precise measurements. The findings will update planetary models and help scientists better study gas giants beyond our solar system.

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Scientists have revised long-held measurements of Jupiter using fresh spacecraft data, revealing the solar system’s largest planet is slightly smaller and flatter than previously believed, according to new research published in Nature Astronomy on Feb. 2.

For decades, Jupiter’s size and shape were based on measurements gathered during brief flybys by NASA’s Pioneer and Voyager missions during the 1970s. Those early observations formed the foundation for planetary textbooks and scientific models worldwide. Now, data from NASA’s Juno spacecraft has allowed researchers to refine those figures with far greater precision, reshaping scientific understanding of the giant planet’s interior.

How Juno Changed Jupiter Measurements

Juno has orbited Jupiter since 2016, repeatedly passing close to its cloud tops while sending radio signals back to Earth. Scientists tracked how those signals bent as they travelled through Jupiter’s dense atmosphere before disappearing behind the planet. This bending revealed subtle distortions caused by powerful winds and atmospheric motion.

Using these observations, researchers calculated Jupiter’s polar radius as 66,842 kilometres, making it about 12 kilometres smaller than earlier estimates. The planet’s equatorial radius was also revised downward by roughly 4 kilometres. Though the changes appear minor, researchers say they significantly improve the accuracy of planetary models.

Yohai Kaspi of Israel’s Weizmann Institute of Science said the findings mean scientific references must now be updated. He explained Jupiter itself has not changed, only humanity’s ability to measure it precisely. The improved measurements reduce long-standing uncertainties that complicated models of Jupiter’s deep interior.

Why Small Differences Matter Scientifically

Jupiter’s vast size and rapid rotation cause it to bulge at the equator while flattening at the poles. Even slight errors in size estimates affect calculations of gravity, density, and internal structure. According to study co-author Eli Galanti, shifting the radius by only a few kilometres allows models to align better with observed gravity and atmospheric data.

These refinements help scientists understand how Jupiter’s internal layers move and interact. They also offer insights into how gas giants form and evolve over time. Jupiter is believed to be the first planet formed in the solar system, making it a crucial reference point.

What This Means Beyond Jupiter

The updated measurements extend beyond Jupiter alone. Astronomers use Jupiter as a template when studying gas giants orbiting distant stars. More accurate Jupiter data improves interpretations of exoplanet observations, especially when analysing size, mass, and atmospheric behaviour.

Researchers say Juno’s radio science technique demonstrates how long-term missions can reshape basic planetary knowledge. As Juno continues collecting data, further refinements may follow. For now, scientists say the findings highlight how even familiar worlds can still surprise, once measured with better tools and deeper patience.