The planet Jupiter, a gas giant and the king of our Solar System, has just been measured as slightly smaller than what is reported in astronomy textbooks.
This might require an update of reference works, as indicated by Yohai Kaspi of the Weizmann Institute in Israel. In reality, Jupiter has not changed shape, but the tools for probing it have significantly improved. New calculations indicate a reduction of about eight kilometers (5 miles) at the equator and around twenty kilometers (12.4 miles) at the poles compared to previous estimates.
An artist's impression of Juno near Jupiter.
Credit: NASA/JPL-Caltech.
This increased precision is the result of the work of the Juno probe, which has been orbiting Jupiter since 2016. During its occultations, when it passes behind the planet, the spacecraft sends radio signals toward Earth. By analyzing how the Jovian atmosphere deflects these waves, scientists can map the shape and size of the giant with great detail. This method, called radio occultation, allows for the reconstruction of temperature and density profiles.
Before Juno's arrival, only six measurements were available, inherited from the Pioneer and Voyager missions in the 1970s. The probe has multiplied data points by adding twenty-six additional observations. Its particular orbit and close flybys of the Galilean moons have made it possible to obtain a much more complete picture, leading to a consolidated analysis.
The processing of this information was made possible thanks to the work of Maria Smirnova, also at the Weizmann Institute. She developed the methods to exploit Juno's raw data. Tracking the bending of radio signals led to improved maps, revealing elements about the planet's internal structure. This approach has thus transformed our perception of Jupiter's actual shape.
Although the adjustments are on the order of only a few kilometers, their scope is notable. Eli Galanti, who led the study, explains that these slight modifications help Jupiter's internal models better align with gravity and atmospheric data. A more precise dimension indeed allows for refining estimates concerning the density and composition of the deep layers.
Understanding Jupiter with more accuracy has an interest that goes beyond our solar system. This planet serves as a reference model for studying gas giants orbiting other stars. A more accurate modeling of its interior thus helps astronomers interpret the properties of distant exoplanets.
These results are the subject of a publication in the journal
Nature Astronomy on February 2nd.
Why a few kilometers matter
The slight size adjustments have direct implications for modeling Jupiter's interior. Primarily composed of hydrogen and helium, the planet has a still-debated internal structure, with a potentially rocky core. Refined dimensions allow for better estimation of the distribution of mass and density at depth.
Integrating these new measurements improves the consistency of models with gravity data collected by Juno. This harmonization helps specify the characteristics of internal layers, such as pressure, temperature, or composition, and allows for a better understanding of the dynamics of currents and the magnetic field.
These advances are particularly useful because Jupiter serves as a comparison point for gas giants discovered elsewhere in the Galaxy. A finer understanding of its internal architecture facilitates the interpretation of observations concerning similar worlds, without requiring an in-situ mission.
In the end, every kilometer counts in the search for maximum precision. By readjusting Jupiter's size, researchers can test the robustness of theories on the formation and evolution of gas planets.