Recent findings suggest Jupiter is not as large as previously believed, based on over four decades of radius measurements.

As a gas giant, Jupiter lacks a solid outer shell like Earth. Nevertheless, astronomers determine its shape by examining how the gas height varies around Earth at a consistent pressure level.

The most accurate measurements of this gas pressure level date back to NASA’s Voyager and Pioneer missions over 40 years ago. These spacecraft utilized radio waves to transmit signals through Jupiter’s atmosphere to Earth, allowing scientists to gather data and compute gas pressure at specific altitudes, employing a method known as radio occultation.

Currently, Eli Garanti from the Weizmann Institute of Science in Israel and his team have been measuring Jupiter’s radius since 2016, using radio occultation data obtained from NASA’s Juno spacecraft, which has been orbiting the gas giant since that year. They report that Jupiter’s average size is approximately 8 kilometers less than previously estimated, particularly at the poles.

“According to the Juno Radio occultation, Jupiter is smaller and more oblate, with a reduced size at the equator,” Garanti mentioned at the Europlanet Science Congress (EPSC) held in Helsinki, Finland on September 11.

Garanti and his team conducted 13 radio occultations with Juno, compared to the six combined by the Voyager and Pioneer missions, and calculated the diameter based on known wind speed measurements of Jupiter. For a pressure equivalent to one bar of gas (Earth’s sea-level atmospheric pressure), the planet’s diameter was measured to be 142,976 kilometers at the poles and 133,684 kilometers at the equator.

“Understanding the exact radius is essential, but it also aids in revealing the inner workings of the planet,” noted Oded Aharonson at the Weizmann Institute of Science, who did not participate in this study. “These new constraints will enable more accurate models of Jupiter’s interior, which are often complex and challenging to explore.”