When you look at Jupiter through a backyard telescope, you’re basically seeing a giant, striped marble of gas. It looks soft. Peaceful, even. But underneath those swirling bands of ammonia and sulfur lies a structural mystery that has kept planetary scientists awake at night for decades. If you were to drop a probe into the center of the planet, what would it actually hit? For a long time, the textbook answer was simple: a solid, rocky ball about the size of Earth.
It turns out that's probably wrong.
Recent data from NASA’s Juno mission has flipped our understanding of what is the core of Jupiter made of on its head. Instead of a neat, compact sphere of rock and ice, Jupiter likely has what scientists call a "dilute" or "fuzzy" core. Imagine a ball of lead that has partially dissolved into a thick soup. It's weird. It’s chaotic. And it changes everything we thought we knew about how planets form.
The old "Rock and Ice" myth vs. the fuzzy reality
We used to think Jupiter formed like a bigger version of Earth. The theory was that a solid core of rock and ice coalesced first, reaching about 10 times the mass of Earth, and then its gravity got so intense that it vacuumed up all the surrounding hydrogen and helium gas from the early solar nebula. This is the classic core-accretion model.
But Juno changed the game.
When the Juno spacecraft arrived at Jupiter in 2016, its job was to map the planet’s gravitational field with extreme precision. By measuring how the spacecraft sped up and slowed down by tiny fractions as it passed over different latitudes, researchers like David Stevenson from Caltech and Yamila Miguel from Leiden Observatory realized the gravity wasn't "pointing" to a small, dense point in the center.
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Instead, the heavy elements—the stuff that isn't hydrogen or helium—seem to be spread out across nearly half the planet's diameter. It's not a hard boundary. There is no "surface" to the core. It’s a gradient where the center is rich in heavy elements but gradually blends into the outer layers.
What is the core of Jupiter made of at the atomic level?
Even if the core is fuzzy, the ingredients are still there. We’re talking about "heavy elements," which in astronomy-speak means anything heavier than helium. Specifically, we're looking at a cocktail of:
- Silicates and Iron: The same stuff that makes up the Earth’s mantle and core.
- Water Ice, Ammonia, and Methane: Often referred to as "ices," though at these pressures, they don't look like ice cubes in your freezer.
- Metallic Hydrogen: This is the real star of the show.
Most of Jupiter’s interior is made of liquid metallic hydrogen. It only exists because the pressure inside Jupiter is millions of times greater than the pressure at Earth’s sea level. Under these conditions, hydrogen atoms are squeezed so tightly that their electrons are squeezed out, allowing them to flow freely. This makes the hydrogen act like a metal. It conducts electricity. It’s the reason Jupiter has such a massive magnetic field.
In the core, this metallic hydrogen is mixed with the rock and ice. It’s a hot, high-pressure slurry. If you were there, you wouldn't be standing on a rock. You'd be crushed and vaporized into a plasma-like soup that is hotter than the surface of the sun.
The "Giant Impact" theory: Why is it so messy?
Why isn't the core a solid ball? One of the leading theories, published in Nature by Shang-Fei Liu and his team, suggests that Jupiter suffered a catastrophic head-on collision about 4.5 billion years ago.
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Imagine a "protoplanet" about ten times the mass of Earth slamming directly into Jupiter’s center.
The impact would have been violent enough to shatter the original solid core and mix its heavy elements with the surrounding hydrogen. If this happened early in the solar system's history, the core might still be trying to settle back down today. But because the interior is so viscous and the heat is so intense, that "mixing" has stayed stuck in a state of dilute chaos for billions of years.
The pressure is literally unimaginable
To understand the core, you have to respect the pressure. At the center of Jupiter, the pressure is estimated to be around 40 to 100 million atmospheres.
Temperature? Around 30,000 to 35,000 degrees Celsius.
At these extremes, the chemistry we learn in high school breaks. Materials that shouldn't mix suddenly do. This is why the "fuzzy core" is so scientifically plausible—under those conditions, the "solids" might actually dissolve into the metallic hydrogen. It's a bit like putting a spoonful of sugar into hot tea; eventually, you don't have a pile of sugar and a cup of tea, you just have sweet tea. Jupiter is just a very big, very hot, very metallic cup of tea.
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Why this actually matters for us on Earth
You might wonder why we spend billions of dollars sending probes to figure out if a gas giant has a "fuzzy" center.
It's because Jupiter is the "Big Brother" of the solar system. It was the first planet to form. Its gravity dictated where Mars ended up, how big the asteroid belt is, and whether or not Earth got bombarded with water-rich comets (giving us our oceans).
If Jupiter has a dilute core, it means the early solar system was a much more violent and chaotic place than our neat computer models suggested. It also helps us understand the thousands of "Exojupiters" we’re finding around other stars. If they all have fuzzy cores, our theories on how planets grow need a total rewrite.
Things to keep in mind about Jupiter's interior:
- There is no "landing" on Jupiter. You’d sink through the clouds, get crushed by the pressure, and eventually become part of the metallic hydrogen soup long before you reached the core.
- The core is shrinking (maybe). Some models suggest the heavy elements are slowly raining down toward the center, but the process is incredibly slow.
- The magnetic field is the key. The way the core is structured drives the dynamo that creates Jupiter's radiation belts. If the core were different, Jupiter wouldn't be the radiation-spewing monster it is today.
What's next for Jupiter exploration?
We aren't done yet. Juno is still orbiting, dipping low and gathering more gravity data. Scientists are also looking toward the JUICE (JUpiter ICy moons Explorer) mission and Europa Clipper. While these are focused on the moons, the way they interact with Jupiter's gravity and magnetic field will give us indirect clues about what's happening in the deep interior.
The more we learn, the more we realize that Jupiter isn't just a ball of gas. It's a complex, multi-layered engine that is still cooling down and settling after a birth that was likely defined by a massive, planet-shattering collision.
Actionable Insights for Space Enthusiasts
If you want to stay updated on the evolving science of Jupiter's core, start by following the Juno Mission's "Image of the Day" and the Southwest Research Institute (SwRI) updates, as they lead the Juno science team. For a deeper dive, look for papers by Scott Bolton, the principal investigator of Juno, who frequently discusses the "dilute core" findings in public lectures. Understanding the core of Jupiter isn't just about one planet; it's about checking the "receipt" for how our entire solar system was built. Keep an eye on the upcoming data releases from Juno’s extended mission, which will focus more on the planet's poles and internal rings to further refine these gravity models.