The most colossal celestial body within our Solar System has undergone a slight reduction in perceived dimensions. While not a physical alteration, our estimations of Jupiter’s size have been refined, revealing a marginally smaller volume than previously understood.
Corroborating the latest findings, Jupiter’s equatorial radius is now documented at 71,488 kilometers (44,421 miles), with its altitudinal extent from the planetary center to its northern pole measured at 66,842 kilometers. This translates to a reduction of 4 kilometers in width on each side at the equator and an apparent flattening of 12 kilometers at each pole compared to earlier assessments.
While this adjustment is not dramatic, it carries significant implications for our scientific models.
“These minor discrepancies in kilometers carry weight,” states Eli Galanti, a planetary scientist affiliated with the Weizmann Institute of Science in Israel.
“A subtle shift in the radius allows our models of Jupiter’s internal structure to align more effectively with both gravitational data and atmospheric observations.”
Our prior determinations of Jupiter’s magnitude and form were predicated on data acquired during NASA’s Voyager and Pioneer missions in the 1970s. These missions employed a technique known as radio occultation (RO). In essence, as the spacecraft transmitted signals back to Earth from behind Jupiter, the massive gaseous envelope of the planet caused some of the signals to refract. Quantifying this refraction allowed for the calculation of the planet’s dimensions.
The available RO measurements for astronomers were confined to just six instances until the present period.
In 2021, NASA repositioned the Jupiter probe Juno into a novel orbital trajectory, facilitating its passage behind the planet from Earth’s vantage point for the first time. This maneuver provided scientists with the opportunity to conduct regular RO measurements, augmented by contemporary data processing methodologies.
“We meticulously tracked the deflection of radio signals as they traversed Jupiter’s atmosphere. This enabled us to translate this information into precise cartographic representations of Jupiter’s temperature and density, yielding the most lucid depiction to date of the giant planet’s scale and configuration,” explains Maria Smirnova, a planetary scientist at the Weizmann Institute.
The powerful atmospheric currents that encircle the gas giant were a factor that earlier estimations of Jupiter’s size had to disregard. However, subsequent research has provided measurements of these winds, allowing Galanti and his collaborators to incorporate this vital data into their revised calculations.
A variation of 4 or 12 kilometers might initially seem insignificant, but achieving greater accuracy in these measurements offers profound insights into the nature of gas giants, both within our Solar System and in exoplanetary systems.
This scientific endeavor has been formally published in the esteemed journal Nature Astronomy.
