Jupiter is smaller and more squashed than we thought

In a significant update on our understanding of the solar system’s largest planet, recent measurements have shown that Jupiter is not as large as we once believed. This marks the first substantial assessment of its dimensions in over 40 years.

Jupiter, a gas giant, lacks a solid surface like Earth, yet its shape can still be evaluated by monitoring the fluctuation of gas height at specific pressure levels. This method is akin to determining sea level on Earth.

The last major data collection regarding Jupiter’s atmospheric pressure was accomplished by NASA’s Voyager and Pioneer missions four decades ago. These spacecraft employed radio waves to assess Jupiter’s atmosphere and calculate gas pressure at various altitudes through a technique known as radio occultation.

Now, a team led by Eli Galanti at the Weizmann Institute of Science has utilized data from NASA’s Juno spacecraft, operational in orbit around Jupiter since 2016, to make new measurements. Their findings indicate that Jupiter is approximately 8 kilometers smaller in diameter than previously estimated, displaying a more pronounced flattening at the poles, contributing to a more oblate shape.

“Thanks to Juno’s radio occultation data, we have discovered that Jupiter is more oblate and about 4 kilometers smaller at the equator,” Galanti reported during the Europlanet Science Congress (EPSC) in Helsinki, Finland, on September 11.

The team conducted 13 radio occultation measurements with Juno, a significant increase from the six total conducted by both Voyager and Pioneer. By integrating known wind speed measurements on Jupiter, they calculated the planet’s dimensions. According to their research, Jupiter’s equatorial diameter measures around 142,976 kilometers while its polar diameter is about 133,684 kilometers.

These measurements not only refine our knowledge of Jupiter’s current dimensions but also contribute to a deeper understanding of its internal structure. As Oded Aharonson, a colleague at the Weizmann Institute, explained, “It’s crucial to understand not just the radius, but also Jupiter’s internal processes. Enhancing our models of the planet’s interior is essential because it remains a mystery that is challenging to unravel.”

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