The planet Jupiter is smaller and flatter than astrophysicists have believed for over 50 years, the Weizmann Institute of Science and NASA discovered.
The study, published in the peer-reviewed journal Nature Astronomy on February 2, 2026, found that Jupiter is about 8km less wide at the equator, and 24km flatter at the poles.
It doesn’t sound like much difference for a planet that is approximately 143,000km wide and 134,000km pole-to-pole, but “these few kilometers matter,” explained Dr. Eli Galanti, a senior staff scientist on the research team.
“Shifting the radius by just a little lets our models of Jupiter’s interior fit both the gravity data and atmospheric measurements much better.”
Why are these measurements different from previous ones?
Lead researcher Prof. Yohai Kaspi explained that earlier measurements didn’t account for Jupiter’s powerful winds. As previous calculations included the extreme winds in their measurements of Jupiter, there were long-standing discrepancies in the measurements.
The new research carried out by the Weizmann team utilized radio signals to map Jupiter’s atmosphere. As the radio waves pass through its atmosphere, they bend, allowing the team to create detailed maps of Jupiter’s temperature and density.
The team used Juno, a NASA spacecraft that was launched in 2011 and has been orbiting Jupiter since 2016. In 2021, NASA extended Juno’s mission, expanding its path and allowing it to pass along the far side of Jupiter from Earth.
This creates new opportunities to measure Jupiter as radio signals from Juno now have to pass directly through Jupiter to reach Earth.
Juno’s Principal Investigator Dr Scott Bolton, explained that “when the spacecraft passes behind the planet, its radio communication signal is blocked and bent by Jupiter’s atmosphere. This enables an accurate measurement of Jupiter’s size.”
The Juno team at the Weizmann seized the opportunity to create the clearest picture yet of the giant gas planet’s size and shape.
This research is an exciting scientific collaboration between the US and Israel to advance our understanding of our solar system.
What’s the significance of this discovery?
Jupiter stands as the largest planet in the solar system, with a surface gravity of approximately 25m/s². Its gravitational pull helps protect Earth from comets and asteroids that could otherwise collide with our planet.
Its gravitational field is also considered to have halted the inward migration of other planetary bodies, allowing Earth to form at its current location.
Prof. Kaspi said, “This research helps us understand how planets form and evolve - Jupiter was likely the first planet to form in the solar system, and by studying what’s happening inside it, we get closer to understanding how the solar system, and planets like ours, came to be.”
The techniques developed in these studies will serve the team in future analyses. The European Space Agency launched Juice, an unmanned mission to explore Jupiter’s icy moons, in 2023, and the techniques developed for this research will be used in combination with the Israeli technology onboard Juice to gain a deeper view into the planet’s atmosphere.