Jupiter, long enshrined in classroom diagrams as a near-perfect striped sphere, has just been resized and reshaped. New measurements from NASA’s Juno spacecraft show the gas giant is slightly smaller and more flattened than standard references have claimed, forcing scientists to redraw one of the Solar System’s most familiar worlds. The findings do more than correct a textbook figure, they sharpen our view of how giant planets form, spin and evolve.
The revision is precise enough that planetary scientists are already talking about a quiet revolution in how they model Jupiter’s interior and compare it with distant exoplanets. By pinning down the planet’s true dimensions and subtle squashing, the Juno team has turned what used to be an educated estimate into a carefully measured number, and in the process revealed that even our best known planets can still surprise us.
Juno’s close passes rewrite Jupiter’s basic stats
The key to the new result is proximity. Instead of relying on telescopic images and indirect modeling, researchers used NASA’s Juno spacecraft, which has been looping around Jupiter in a highly elongated orbit, to track how the planet’s gravity tugs on a radio signal. As Juno skimmed close to the cloud tops on repeated flybys, tiny shifts in the frequency of its radio transmissions revealed exactly how massive Jupiter is at different latitudes and how its bulk is distributed. That radio science experiment effectively turned the spacecraft into a tape measure for a world more than 600 million kilometers away.
Earlier this year, an international team reported that those measurements show Jupiter is not quite as large as standard reference values suggested. Using advanced radio science data from the mission, scientists calculated the equatorial diameter at 88,841 miles, and found that the polar regions are even more compressed than expected. That means the planet’s average radius is smaller, and its overall shape more oblate, than the figures that have long circulated in planetary fact sheets. For a world already known as the Solar System’s heavyweight, shaving off a few kilometers in radius may sound minor, but at this scale it represents a major refinement in our understanding of its structure.
How radio occultations exposed a “squashed” giant
The new work hinges on a technique known as radio occultation, in which scientists watch how a spacecraft’s radio signal is bent and delayed as it passes behind a planet. In the latest study, the authors analyzed data from 13 such flybys, using high precision tracking to map Jupiter’s shape with unprecedented accuracy. By combining those occultation profiles with models of the planet’s gravity field, the team could infer not just the size of Jupiter, but how its rotation and internal layering contribute to its flattened appearance. The result is a three dimensional picture that shows a slightly narrower equator and more depressed poles than earlier models allowed.
Researchers describe the planet as more “squashed” because the difference between equatorial and polar radii is larger than previously believed. One analysis notes that Jupiter is smaller on average by several kilometers, with the reduction especially pronounced near the poles, while the equator is slightly narrower than standard values. Earlier work had already hinted at an 8 kilometre adjustment, and the new Juno based mapping confirms that trend with far greater precision. For a gas giant whose visible “surface” is really a layer of clouds, pinning down that boundary is tricky, but the radio occultation method effectively defines a reference level in the atmosphere and measures the planet’s figure relative to it.
Inside the Nature Astronomy analysis of Jupiter’s figure
The most detailed account of the new measurements appears in a study in Nature Astronomy, which lays out how the team turned raw radio tracking into a refined planetary profile. The researchers combined Juno’s gravity data with models of how a rapidly rotating fluid planet should deform, then iterated until the theoretical shape matched the occultation results. That approach allowed them to test whether Jupiter’s deep interior behaves like a simple rotating fluid or whether strong winds and density variations distort the planet more than expected. The answer, within the uncertainties, is that Jupiter is remarkably close to the idealized case.
In technical terms, the study concludes that the planet’s deep atmosphere is nearly barotropic, showing minimal vertical variation in density at a given pressure level. That means the fierce jet streams and storms that dominate Jupiter’s visible cloud tops do not significantly warp the planet’s overall figure at depth. For modelers, this is a crucial constraint, because it supports the use of relatively simple interior structures when calculating how mass is layered inside the planet. It also implies that the newly measured flattening is driven mainly by rotation and bulk composition, not by exotic internal flows that would complicate the picture.
From “textbooks will need to be updated” to global reaction
The idea that “textbooks are wrong” about Jupiter is not just a catchy line, it reflects how entrenched the old numbers had become. For decades, planetary science references, from university handbooks to children’s atlases, relied on values derived from earlier spacecraft and Earth based observations. The Juno team’s announcement that the planet is slightly smaller and more compressed at the poles prompted immediate calls to revise those entries. One report on the findings highlighted how an image of Jupiter from NASA, paired with the new measurements, underscores the gap between the familiar illustrations and the more precise reality.
Scientists involved in the work have been careful to stress that the change does not dethrone Jupiter as the Solar System’s largest planet, but it does refine the baseline for every comparison that follows. A separate analysis noted that they found Jupiter is around 8 kilometres smaller on average than earlier estimates, a shift large enough that precision minded educators and data compilers will need to update their tables. For the public, the change is subtle enough that Jupiter will look the same through a backyard telescope, but for researchers, it is a reminder that even seemingly basic planetary facts are subject to revision when better data arrive.
Techniques, teams and what a flatter Jupiter tells us
Behind the headline figures is a story of technical ingenuity and international collaboration. The Juno radio science experiment relies on exquisitely stable transmitters and receivers, along with careful tracking of the spacecraft’s motion as it dives through Jupiter’s intense radiation belts. One member of the team, PhD student Maria Smirnova, developed a specialized technique to process the new radio data, improving the way scientists separate the planet’s gravitational pull from other forces acting on the spacecraft. That refinement made it possible to match the occultation profiles with models of Jupiter’s atmosphere and interior far more tightly than before.
Other groups have emphasized how the new shape measurement fits into a broader effort to understand giant planets. A report from NASA notes that data from Juno are helping scientists refine models of exoplanets in other star systems, since Jupiter serves as a benchmark for gas giants everywhere. Another analysis from research of Jupiter points out that the planet is narrower at the equator than previously thought, a detail that feeds directly into calculations of how fast it rotates and how its interior responds to that spin. Together, these studies show that getting Jupiter’s size and shape right is not a cosmetic tweak, it is a foundation for understanding giant planets across the Solar Syste and beyond.
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