For more than half a century, scientists believed they had a solid grasp of Jupiter’s size and shape.
As the largest planet in the solar system, Jupiter has long served as a benchmark for understanding gas giants.
Now, new research suggests that our picture of this massive world needs a small but important update.
In a study published in Nature Astronomy, researchers from the Weizmann Institute of Science led an international team that produced the most precise measurement yet of Jupiter’s shape.
Using new data from NASA’s Juno spacecraft, they found that Jupiter is slightly narrower at the equator and more flattened at the poles than earlier estimates suggested.
Professor Yohai Kaspi, who led the research, explains that in theory, measuring a planet’s size is straightforward. If you know how far away it is and how fast it rotates, you can work out its shape.
The challenge comes when you want extreme accuracy. Until now, Jupiter’s official dimensions were based on just six measurements collected nearly 50 years ago by NASA’s Voyager and Pioneer missions.
That changed with NASA Juno, which has been orbiting Jupiter since 2016. When NASA extended Juno’s mission in 2021, the spacecraft was placed on a new orbit that allowed it to pass behind Jupiter from Earth’s point of view.
During these moments, Jupiter’s atmosphere bends and blocks Juno’s radio signals, creating a rare opportunity to measure the planet’s size with exceptional precision.
The Weizmann-led team analyzed 26 of these new measurements.
By tracking how the radio signals changed as they passed through Jupiter’s atmosphere, the researchers could map the planet’s temperature and density in detail. The result was a clearer and more accurate picture of Jupiter’s true shape.
Their findings show that Jupiter is about 8 kilometers narrower at the equator and roughly 24 kilometers flatter at the poles than previously thought.
While these differences may sound tiny compared to Jupiter’s enormous size, they matter a great deal for science. Small changes in radius help scientists build much better models of the planet’s interior, allowing gravity data and atmospheric observations to finally line up.
The new measurements also account for something earlier studies largely ignored: Jupiter’s extreme winds.
These powerful jet streams and massive storms affect the planet’s shape, and including them helped resolve long-standing inconsistencies in earlier calculations. The radio data even offer clues about how deep these winds and giant cyclones extend beneath Jupiter’s cloud tops.
Understanding Jupiter’s structure goes beyond curiosity. As the first planet to form in the solar system, Jupiter played a major role in shaping everything that came after, including Earth.
Learning how it formed and how its atmosphere connects to its deep interior helps scientists understand how planets evolve, both in our solar system and around other stars.
Looking ahead, the techniques developed in this research will also be used to study new data from the European Space Agency’s upcoming Jupiter mission, helping scientists refine our view of the giant planet even further.
Source: Weizmann Institute of Science.
