Jupiter, the largest planet in our solar system, is a world of extremes. For decades, the composition and structure of its interior remained one of the most significant mysteries in planetary science. Specifically, the nature of its central region—whether it contains a dense, solid, rocky core—has been a subject of intense theoretical debate. Recent scientific findings, primarily driven by a dedicated NASA mission, have provided unprecedented insights, fundamentally changing our understanding of the giant planet’s deep structure.
Understanding Jupiter’s Internal Layers
Jupiter’s structure begins with a vast, swirling atmosphere composed primarily of hydrogen and helium, similar to the composition of the Sun. As the atmospheric gases are compressed under the planet’s immense gravity, they transition into a liquid state without a distinct surface boundary. Deep below the cloud tops, the pressure increases exponentially, eventually forcing the hydrogen into a supercritical fluid state.
At a depth roughly 7,000 kilometers below the cloud tops, the pressure becomes so extreme that it strips the electrons from the hydrogen atoms. This process creates a massive, electrically conductive fluid known as liquid metallic hydrogen. This dense, exotic layer acts as the planet’s mantle and is responsible for generating Jupiter’s incredibly powerful magnetic field. The center of Jupiter, beneath this metallic layer, is where the core material is located.
The Current Scientific Consensus on Jupiter’s Core
The traditional model of Jupiter’s interior proposed a small, dense, and sharply defined core made of rock and ice at the planet’s center. This conventional idea suggested a compact, terrestrial-style core of heavy elements. However, data from the NASA Juno mission has shown that the reality is far more complex than this simple, layered structure. The new consensus is that Jupiter does not possess a small, solid, well-defined rocky core with distinct boundaries.
Instead, Jupiter’s central region is now described as a “diluted” or “fuzzy” core. This structure is a vast region where the heavy elements—rock, metal, and ice—are not cleanly separated but are mixed and blended with the overlying layer of liquid metallic hydrogen. The heavy elements are spread out over a significant fraction of the planet’s radius, extending much farther than previously hypothesized.
The total mass of heavy elements concentrated in this fuzzy core is substantial, likely ranging from several times the mass of Earth up to a few dozen Earth masses. While the core contains materials that would be classified as rock and ice under normal conditions, the extreme temperatures and pressures inside Jupiter mean these materials exist in exotic, super-compressed states. The observation of this diluted structure has challenged long-standing theories about how giant planets form, suggesting a more tumultuous or gradual formation process than previously assumed.
How Scientists Determined the Core Structure
The revolutionary understanding of Jupiter’s core was made possible by the NASA Juno spacecraft, which arrived at the planet in 2016. Juno’s primary method for probing the interior was the precise measurement of Jupiter’s gravitational field. A planet’s gravitational field is not uniform; it contains subtle variations that depend on how mass is distributed inside the planet.
Scientists used a technique called radio science, which involves tracking the minute changes in the spacecraft’s velocity as it orbits Jupiter. As Juno flew close to the planet’s cloud tops, variations in the local gravitational pull caused tiny shifts in the spacecraft’s speed, sometimes as small as 0.01 millimeter per second. These speed changes were detected by monitoring the Doppler shift in radio signals sent between the spacecraft and the Deep Space Network antennas on Earth. The data collected from multiple, close-in orbits provided a high-resolution map of the planet’s gravitational field.
The gravitational signature revealed that the mass distribution within Jupiter was less centrally concentrated than models predicting a compact, solid core had suggested. The data indicated a large, uneven distribution of mass in the deep interior, which was the definitive evidence for a fuzzy core that gradually blends into the outer layers.