We've Finally Seen Inside Jupiter | Juno's Year 8 Discovery

Think you know Jupiter? The colossus of our solar system. The king of the gas giants. For a long time, science believed it had a pretty good idea of what was inside. But the truth is that, for decades, there was a silent war among astronomers over the heart of this giant. The debate was heated. Did Jupiter have a solid rocky core, or was it just a colossal ball of gas with nothing solid in the center? In 2017, however, this discussion was abruptly ended. A bold NASA mission changed the game and proved that both sides were wrong. The data revealed a third option that no one, absolutely no one, expected. Jupiter's heart is not solid. But it is not missing either. The best definition we have found is it is fuzzy. It is like a diluted or spongy core. And as simple as that may sound, this discovery is a gigantic problem for science. It implodes almost everything we thought we knew about how Jupiter formed, what its interior is like, and, curiously, why its magnetic field is so bizarre. To understand what a shock the Juno probe's discovery was, we need to go back a bit and understand the two theories that dominated astronomy for years. They tried to explain how a monster like Jupiter emerged from the chaos of the young solar system. The first theory is called gravitational collapse. Supporters of this idea suggest that Jupiter formed directly and quickly. An immense cloud of gas would have collapsed under its own gravity in the cold, outer regions of the solar system. Then, it would have migrated to where it is today. In this scenario, Jupiter would be like a layer cake made entirely of churning gas, from the top of the clouds down to the exact center, with no rock, with no metal, just gas. But this explanation did not convince everyone. There was a second theory, much more widely accepted, that said almost the opposite. The core accretion theory argued that Jupiter started with a solid heart. Billions of years ago, heavy elements like carbon, nitrogen, oxygen, magnesium, silicon and iron would have clumped together. As this rocky and metallic core grew, its gravity became stronger. Eventually, this core became so massive that it began to voraciously capture the surrounding hydrogen and helium, accumulating layers upon layers of gas over millions of years until it became the planet we see today. Intuitively, this makes a lot of sense. Our planetary formation models indicate that, in the outer parts of the solar nebula, ice and rock would condense first. These solid planetary embryos, as they migrated inward, would use their gravity to trap the gases. Therefore, the core accretion model predicted something very specific. Jupiter should have a dense, compact, well-defined core with a clear boundary separating the solid center from the outer layers of gas. Science needed a verdict, and to get it, we sent scouts. The first missions that visited Jupiter tried, each in its own way, to peek at what was beneath that dramatic and colorful atmosphere. In the 1970s and 1980s, the voyagers and pioneers led the way. In the 1990s, with the accumulated data, scientists already knew something crucial. Jupiter was rich in heavy elements. This meant it was not made just of hydrogen and helium. There was something else inside. Then came the Galileo mission. It brought a fundamental piece of the puzzle. Galileo found evidence that Jupiter's monstrous magnetic field needed to be generated by an inner layer of liquid metallic hydrogen. This created a paradox. Think about it. Standard theories require a solid core to initiate gas capture. But if the data showed that the interior was essentially liquid, how did Jupiter form in the first place? Did it ever have a solid core and somehow lose it? If so, how did that happen? Was all our knowledge about the formation of gas giants completely wrong? Despite the success of these early missions, Jupiter's internal structure remained a frustrating mystery. The data did not have enough precision to settle the matter. Was the core solid or diffuse? What exactly was it made of? How did it generate that colossal magnetic field? All we had were educated guesses. Until Juno arrived. Juno's main objective was ambitious. To get as close as possible to the truth about Jupiter's composition. And the strategy to do this was not to take colorful pictures, but to measure, with unprecedented precision, the planet's gravitational and magnetic fields. Unlike Galileo, Juno was built specifically to map Jupiter's gravity. We are talking about a map 100 times more detailed than anything we had before. When it entered the planet's orbit on July 4th, 2016, it began a highly elliptical polar trajectory. The probe dove aggressively, passing just 4,200 kilometers from the top of Jupiter's clouds. It repeated this dive dozens of times from several different angles. This route made the probe an incredibly sensitive instrument to the smallest variations in Jupiter's gravity. But, you might ask, why are we so interested in gravity? What does that have to do with what is in the center of the planet? Well, we usually see gravity represented as a perfectly round cone, equal on all sides. I am sorry to say, but this diagram is an oversimplification. For a planet's gravity to be completely uniform like this, the mass distribution inside it would also have to be perfectly uniform. A perfect sphere of a single density. In reality, if we took an extreme zoom, the gravitational fields of the planets would be irregular. Planets are made of many different elements and materials. Each has its own mass, density, and distribution. On Earth, for example, gravity is slightly different if you are over a mountain range or over an oceanic plain. These internal differences are reflected as tiny, almost imperceptible variations in the gravitational field. And that is exactly why scientists are so obsessed with mapping Jupiter's gravity. Understanding these variations is like taking an x-ray of the planet's interior. But how does Juno measure this? With pure physics. As Jupiter's gravity fluctuates, it pulls Juno with more or less force. This makes the probe accelerate or decelerate. And Juno is so precise that it can detect speed changes of just 0.01 millimeters per second. It is an unbelievable sensitivity. At the same time, Juno continuously sends a constant radio signal back to Earth. Scientists here on Earth receive this signal and use the famous Doppler effect to decode it. Where gravity is stronger, Juno accelerates, and we perceive a higher frequency radio wave. Where gravity is weaker, it decelerates, resulting in a lower frequency. By repeating this process, dive after dive, scientists were able to build an extremely precise map of Jupiter's gravitational field. A map that directly reflects how the mass is arranged inside. The Galileo mission gave us a chalk drawing of Jupiter's gravity. Juno brought an 8K resolution image. And what this map revealed left researchers' jaws on the floor. The revelation was clear. Both main theories about Jupiter's core were wrong. Juno confirmed that Jupiter does, indeed, have a core. But it is not solid like a rock, as many thought. It is diffuse, nebulous, or, as scientists call it, fuzzy. Instead of being a dense and compact ball with a sharp boundary, this core gradually dissolves, mixing with the hydrogen-rich layers right above it. There is no dividing line. It is a smooth transition from a center rich in heavy elements to a gaseous exterior. And there is more. It is much larger than expected. This fuzzy core extends for about half of Jupiter's entire radius. It is a colossal region. This discovery generated a wave of new questions. The main one. Does our understanding of how Jupiter formed need to be thrown in the trash? A popular theory quickly emerged to try to explain this oddity. The idea is that Jupiter did start with a solid core, according to the Standard Model. But very early in its history, it suffered a catastrophic collision. An impact with another young planet would have been so violent that it shattered and mixed the original solid core with the lighter gases around it. The result of this cosmic blender mix would be the fuzzy core we see today. The problem is that the Standard Model of gas giant formation does not work without a solid core at the beginning to capture the gas. So, either this diffusion of the core happened later, or our basic models are wrong. Either way, to cause this damage, the collision would have had to be massive, possibly with another planet in formation. Scientists speculate that up to half of Jupiter's current core could originate from the remains of this impacting planet. It was an elegant theory, except for a small problem. A team of researchers decided to test this theory using a supercomputer. They wanted to simulate exactly the event that would lead to the result Juno showed. They created several scenarios, varying the size of the invading object, the angle, and the speed of the collision against a proto-Jupiter. But, as hard as they tried, they could not recreate Juno's fuzzy core. Every time the simulation showed the same result, the impact rocked the planet to its core initially. But after a while, the rocky and dense material inevitably settled back in the center, like sediment at the bottom of a glass of water. It did not stay dissolved in the rest of the planet. A sharp boundary reappeared, clearly separating the core from the outer layers of hydrogen. This did not match the Juno data. The mystery continued. It was time to go back to the drawing board. Curiously, the next clue to solve this puzzle did not come from Jupiter, but from its next door neighbor. Well, if you consider a door 648 million kilometers away, we are talking about Saturn. We have known, since 2014, that the waves in Saturn's rings are caused by deep vibrations inside the planet itself. This gives us an unprecedented view of what is going on inside, very similar to how earthquakes allow us to study the interior of the Earth. When researchers combined the gravitational field data from the Cassini probe with these wave measurements in the rings, the result was surprising. Observations showed that at least some deep regions of Saturn's interior do not experience convection. This is a huge discovery. Think about this. Inside a giant planet like Saturn, heat is constantly trying to escape from the center. Normally, this happens through convection. It is what happens in the Earth's mantle, or when you heat a soup. The hot fluid rises to the surface, cools down, and then sinks again, only to be heated and rise again. It is an eternal cycle of mixing. If Saturn were completely convective, it would mix the heavy elements throughout its interior. There would be no dense central region. The entire planet would be a completely mixed, homogeneous soup. But, if it is partially stable against convection, we would expect to see a material gradient. Heavier elements concentrated in the center, gradually decreasing toward the edge. And guess what? That is exactly what the data shows. Researchers published their findings in 2021, arguing that the only way to explain the data from the waves in Saturn's rings, its gravitational field, and its partial lack of convection is that it also has a fuzzy core. And, as if the pieces were finally falling into place, Juno's data also suggests that large regions of Jupiter might not be convective. It seems we are connecting the dots. If both Saturn and Jupiter have fuzzy cores, it is much more likely that this is the result of a common planetary formation process, and not a random and catastrophic collision event. Now, scientists are working on a new emerging theory about how gas giants are born. A theory where fuzzy cores are a natural and expected part of planetary formation. We have not yet reached a perfect and final explanation. But one thing is crystal clear. The old assumptions we had about the largest planets in our solar system were incorrect. Jupiter and Saturn are not made of a solid core surrounded by a gas envelope. Nor do they have a completely mixed interior. Their fuzzy cores are composed of a compositional gradient, with more heavy elements concentrated in the center, which dissolve into the gas envelope without a defined boundary. This complexity and this irregular mixing challenge are current models of planetary evolution, where our old and simplistic model predicted that giants would cool predictably over time. These new models do not follow the same patterns. And this is true not only for our solar system, but for all the gas giant exoplanets we have discovered and studied so far. But while we try to solve the puzzle of the core, there is another fundamental piece that needs to fit into this new reality of a fuzzy core. Jupiter's strange and chaotic magnetic field. For years, science has known that Jupiter's magnetic field is generated through a dynamo process in its metallic hydrogen layer. This layer extends from 20 to 60,000 kilometers deep. There, temperatures can exceed 30,000 Kelvin, and pressures are millions of times greater than on the Earth's surface. In these extreme conditions, hydrogen is in a liquid state. But even more incredibly, the hydrogen electrons become delocalized, meaning they flow freely. This creates an electrically conductive metallic state. Combined with Jupiter's super-fast rotation, this metallic liquid hydrogen creates a dynamo effect. Although the exact process of how this dynamo is powered remains a mystery, one thing is certain. It works. Jupiter has the largest and strongest magnetic field of any planet in the entire solar system. Its magnetosphere spreads from 7 to 21 times the diameter of the planet itself, tapering into a tadpole shape behind it that extends all the way to Saturn's orbit, about 1 billion kilometers away. It is a truly monstrous structure. However, Jupiter's magnetic field also has some very peculiar characteristics. It is much stronger in the northern hemisphere than in the southern hemisphere. It has intense localized magnetic spots, and, bizarrely, it has two magnetic south poles. Scientists hoped that the discovery of Jupiter's fuzzy core could explain some of these strange behaviors. Frustratingly for them, the opposite turned out to be true. The fuzzy core actually complicates the understanding of the magnetic field even more, instead of explaining it. Remember, magnetic fields in planets are usually created by turbulent movements of electrically conductive material, like the convection of metallic liquid hydrogen. However, Juno's data showed that large regions of Jupiter, like Saturn, seem to be at least partially non-convective. Researchers modeled the fluid dynamics of Jupiter's interior in two potentially non-convective regions to see how they would affect the magnetic field, one in the upper part of the planet's interior and the other further down, corresponding to the diluted core. They concluded that the upper stable layer helps explain Jupiter's magnetic field even better than the previous solid core models. However, the lower region, representing the non-convective diluted core, failed to explain the magnetic field on its own. In other words, a completely stable fuzzy core produces a magnetic field very different from the one we actually observe. Now, researchers believe that Jupiter's dynamo is much more complicated than originally thought. It is possible that, below the upper layer of molecular hydrogen, Jupiter has a helium layer, which rains through the liquid hydrogen like oil passing through water. Some think this could have an effect on the magnetic field. Another theory states that Jupiter's dynamo does not operate in a homogeneous way, like on Earth. Instead, the planet's asymmetrical magnetosphere would be the result of variations in density, electrical conductivity, or both. But, overall, no one knows exactly how this magnetic field is produced, or what the exact role of the fuzzy core is in its creation. It is a puzzle with missing pieces. One thing we do know for sure, however, is that Jupiter's magnetic field is responsible for the largest and brightest auroras in the solar system. On Earth, auroras are only visible in a 4-6 month window per year, near the poles. On Jupiter, they never stop. They cover the poles with a dazzling spectacle of ultraviolet colors, hundreds of times more powerful and energetic than the auroras we are familiar with. By stitching together far ultraviolet images from the Hubble imaging spectrograph, scientists were able to create impressive videos of these auroras in action. They are spectacular. Despite Juno's revolutionary discoveries, Jupiter keeps its secrets under lock and key. We still do not know how its fuzzy core really formed, nor do we know how permanent it is. Is the fuzzy core a stable structure that will last for billions of years? Or is it slowly dissolving into Jupiter's gaseous layers? What is its exact relationship with the metallic hydrogen above it, and the resulting magnetic field that Juno mapped? Are fuzzy cores just a natural part of the formation of any gas giant? We cannot say with absolute certainty yet. But one thing is certain, our current models do not show the full picture. Hopefully, with future studies, we will be able to answer these questions one by one. Although history shows us that, the more we learn, the more questions we will continue to ask. The search for truth is relentless. And it is also, perhaps, the most human thing we can do. There is something captivating about Jupiter's colossal and stormy surface. From above, its immensity makes everything seem calm. Its colorful bands, motionless and majestic. But if you dove beneath those vibrant clouds, you would be swallowed by violent storms the size of entire planets. Leave a like, subscribe to the channel, and share. Thanks for watching, and see you in the next video.