Jupiter’s atmosphere is staggeringly thick by any earthly standard. The planet has no solid surface at all, so what we call the “atmosphere” stretches from wispy upper layers down through increasingly dense gas that gradually transitions into a hot, pressurized liquid thousands of kilometers below the visible clouds. The deepest weather-driven winds reach roughly 3,000 kilometers beneath the cloud tops, and below that the hydrogen grows so compressed it behaves like a metal. In a real sense, Jupiter is atmosphere almost all the way down.
There Is No Ground
The single most important fact about Jupiter’s atmosphere is that it never ends in a surface. On Earth, we think of the atmosphere as a blanket of gas sitting on top of rock and ocean. Jupiter has no equivalent boundary. Because there is no solid ground to mark where the atmosphere stops, planetary scientists had to pick an arbitrary reference point. They chose the altitude where pressure equals one bar, roughly the same as sea-level pressure on Earth.1arXiv. Giant planet interiors and atmospheres Everything above that line is loosely “atmosphere” in the traditional sense; everything below it is also gas (or eventually liquid), just denser and hotter with depth.
This is a fundamentally different situation from any rocky planet. On Mars, the atmosphere is a thin shell of carbon dioxide you could measure in a few dozen kilometers. On Earth, the atmosphere thins to near-vacuum by about 100 kilometers up. Jupiter’s gaseous envelope, by contrast, extends tens of thousands of kilometers inward before it smoothly becomes something dense enough to call an interior. The planet’s mean density is only about 1.33 grams per cubic centimeter, less than a quarter of Earth’s, because most of that enormous volume is hydrogen and helium gas under varying degrees of compression.
What the Galileo Probe Encountered
The only spacecraft ever to descend into Jupiter’s atmosphere was the Galileo probe, which plunged in on December 7, 1995. It transmitted data as it fell, surviving until the surrounding pressure reached roughly 24 bars, about 24 times the pressure at Earth’s surface.2PubMed. Galileo probe: in situ observations of Jupiter’s atmosphere At that depth it was around 150 kilometers below the one-bar cloud tops, and the temperature had climbed to over 150°C.
Twenty-four bars sounds extreme, but by Jupiter’s standards the probe barely scratched the surface. The atmosphere continues for thousands of kilometers below where the probe was crushed and vaporized. The probe confirmed that temperatures and pressures rise steeply with depth, with the gas becoming progressively thicker and hotter as you go down. It also found that the atmosphere was drier than expected in the region it sampled, a quirk later attributed to the probe having entered an unusually cloud-free “hot spot” rather than a representative patch of atmosphere.
Layers of Cloud and Chemistry
Jupiter’s visible face is painted by distinct cloud decks stacked at different altitudes, each made of a different substance. The outermost layer, sitting at about 0.5 to 0.7 bars of pressure, is ammonia ice. Below that, around 1.5 to 2.5 bars, sits a layer of ammonium hydrosulfide particles. Deeper still, at roughly 4 to 7.5 bars, comes a water cloud deck whose base depends on how much water Jupiter’s deep atmosphere actually contains.3Icarus. Modeling Jupiter’s cloud bands and decks: 2. Distribution and motion of condensates Simulations consistently reproduce this stacked structure, with the ammonia ice on top and water clouds at the bottom, though the exact altitudes shift depending on assumptions about the deep composition.4Icarus. Simulating Jupiter’s weather layer. Part II: Passive ammonia and water cycles
This three-tiered cloud system spans only a handful of bars in pressure, which translates to a few tens of kilometers in altitude. Compared to the full depth of Jupiter’s gaseous envelope, the cloud decks are a thin skin on the outside. Yet they are where most of the visual drama takes place: the brown belts and white zones, the swirling storms, and the vivid color contrasts that make Jupiter so photogenic are all produced within this relatively narrow band.
Juno’s microwave radiometer has peered far below the clouds by measuring thermal radiation at wavelengths that penetrate to a hundred bars of pressure or more. Those observations revealed that ammonia is not evenly mixed at depth. Instead, ammonia concentrations vary with latitude and altitude in complex patterns, with the equatorial zone appearing closest to a well-mixed ideal.5Geophysical Research Letters. The distribution of ammonia on Jupiter from a preliminary inversion of Juno microwave radiometer data Follow-up work combining Juno and ground-based radio telescope data has refined the deep ammonia abundance, confirming that concentrations at depth are enriched relative to what you would expect from a purely solar-composition mixture.6The Planetary Science Journal. Ammonia Abundance Derived from Juno MWR and VLA Observations of Jupiter
Three Thousand Kilometers of Wind
Jupiter’s banded appearance is driven by powerful jet streams that race around the planet at different speeds and latitudes. From the cloud tops these jets look like surface-level weather features, similar in spirit to Earth’s jet stream. But measurements from the Juno spacecraft revealed something far more dramatic: those winds extend thousands of kilometers into the planet’s interior.
Juno pinned this down by measuring tiny asymmetries in Jupiter’s gravitational field. If the winds were confined to a shallow weather layer, the gravity field would look different from what Juno detected. By inverting the gravity data, researchers calculated that the jet streams plunge to depths of roughly 3,000 kilometers below the cloud level, probably reaching the zone where increasing electrical conductivity begins to brake the flow through interactions with Jupiter’s magnetic field.7Nature. Jupiter’s atmospheric jet streams extend thousands of kilometres deep Independent analyses of Juno’s asymmetric gravity measurements arrived at the same conclusion.8Journal of Geophysical Research: Planets. The Range of Jupiter’s Flow Structures That Fit the Juno Asymmetric Gravity Measurements
Three thousand kilometers of wind is a staggering number. For context, that is nearly half the radius of Earth. And this wind-bearing layer, while it sounds immense, still represents only about one percent of Jupiter’s total mass.7Nature. Jupiter’s atmospheric jet streams extend thousands of kilometres deep The vast bulk of the planet lies deeper still, in a regime where the hydrogen is too conductive and too dense for organized wind patterns to survive.
An interesting comparison: on Saturn, a similar analysis using Cassini gravity data found that zonal flows extend about three times deeper than on Jupiter.9Geophysical Research Letters. Depth Dependent Dynamics Explain the Equatorial Jet Difference Between Jupiter and Saturn Saturn’s lower density and weaker internal magnetic field allow its winds to reach further before being damped. This means that even among gas giants, “thick atmosphere” is a relative term, and the depth of active weather depends on how conditions change with depth in each individual planet.
The Great Red Spot and Storm Depth
Jupiter’s Great Red Spot is a storm wider than Earth, and it has been raging for at least a few centuries. A natural question is how deep a storm like that extends into such a thick atmosphere. Juno answered this by flying directly over the vortex and measuring the subtle gravitational tug created by the density differences associated with the storm’s circulation.
The result was that the Great Red Spot reaches down to about 500 kilometers beneath the cloud tops.10PubMed. The depth of Jupiter’s Great Red Spot constrained by Juno gravity overflights That is deep by terrestrial standards but far shallower than the jet streams. The analysis used data from 12 Juno encounters with the planet, including two overflights directly above the storm, and two independent methods yielded consistent results. A separate study estimated that the methodology could resolve the depth of the storm’s winds to within about 100 kilometers for features in the 300 to 1,300 kilometer depth range.11The Astrophysical Journal Letters. Determining the Depth of Jupiter’s Great Red Spot with Juno: A Slepian Approach
So even a monster storm like the Great Red Spot is shallow compared to the jet streams that frame it. The jets extend six times deeper. And both features are shallow compared to the full gaseous envelope, which continues for tens of thousands of kilometers below. Jupiter’s atmosphere has a layered character: a thin, chemically active weather layer on top, a deep wind zone beneath that, and then the enormous high-pressure interior where winds give way to sluggish convection.
Where Gas Becomes Metal
Below the wind zone, pressure and temperature keep climbing. At some point, the hydrogen gas is squeezed so hard it stops behaving like a molecular gas and starts acting like a liquid metal, conducting electricity the way copper wire does. This transition is a cornerstone of Jupiter’s internal structure.
Laboratory experiments shooting shockwaves through hydrogen samples found that the transition to metallic behavior happens at a pressure of roughly 140 gigapascals in a fluid state.12PubMed. Metallization and electrical conductivity of hydrogen in Jupiter Inside Jupiter, that pressure is reached at a depth of roughly 10,000 to 15,000 kilometers below the cloud tops. Interior models typically describe Jupiter as having three broad layers: an outer region of molecular hydrogen and helium, a deep region of metallic hydrogen, and a central core that may be a mix of heavier elements.13Journal of Geophysical Research: Planets. Understanding Jupiter’s interior
The transition between molecular and metallic hydrogen is not a sharp boundary like a surface. It is gradual, with the electrical conductivity ramping up continuously as pressure increases.14The Astrophysical Journal. The molecular-metallic transition of hydrogen and the structure of Jupiter and Saturn This is part of why asking whether Jupiter’s atmosphere is “thick or thin” becomes philosophically tricky. There is no moment where gas clearly becomes not-gas. You can define the “atmosphere” as the top few hundred kilometers of cloud and visible weather, making it thin. Or you can define it as everything above the metallic hydrogen layer, making it tens of thousands of kilometers thick. Or you can argue, reasonably, that since there is never a solid or liquid surface, the entire planet is atmosphere in some sense.
A Core That May Not Be Solid
Even Jupiter’s core complicates the question. Earlier models assumed a compact rocky or icy core at the center, perhaps 10 to 20 Earth masses of heavy elements packed into a relatively small ball. But Juno’s precision gravity measurements have challenged that picture. The data are better explained by a “dilute core,” a region where heavy elements are mixed into the surrounding hydrogen rather than concentrated in a tight lump, potentially extending outward over a large fraction of the planet’s radius.15Geophysical Research Letters. Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core
If the core is diffuse rather than compact, there is genuinely no distinct solid body at the center of Jupiter. The planet would be gas, liquid, and metallic fluid all the way down, with heavier elements gradually concentrating toward the center but never forming a hard boundary. In that scenario, calling anything inside Jupiter “not atmosphere” becomes a matter of convention rather than physics.
Internal Heat and Convection
Jupiter radiates about 1.6 to 1.7 times more energy than it receives from the Sun. That excess energy comes from the planet’s interior, left over from its formation and from ongoing slow contraction. This internal heat source drives convection throughout the deep atmosphere and interior, carrying energy upward from the hot center to the cloud tops where it escapes as infrared radiation.
This heat flow has consequences for the atmosphere’s structure. Modeling suggests that the ratio of total emitted heat to absorbed sunlight on Jupiter is above a critical value of about 1.27, which means the internal heat is strong enough to smooth out the temperature differences that sunlight alone would create between equator and poles.16Icarus. Solar heating and internal heat flow on Jupiter In other words, Jupiter’s deep interior acts as a giant heat redistributor, so the atmospheric temperature differences between equator and poles at depth are smaller than you might expect from sunshine alone. The planet’s banded, axially symmetric appearance may partly owe itself to this internal heat flow overwhelming the effects of differential solar heating.
This is a stark contrast with Earth, where the atmosphere is heated almost entirely from below by the sun-warmed surface and there is no significant internal heat contribution. Jupiter’s atmosphere is heated from both above and below, and the heat from below is the dominant factor driving the deep circulation.
The Puzzlingly Hot Upper Atmosphere
While most of Jupiter’s atmosphere gets thicker and hotter with depth, the very top of the atmosphere has its own puzzle. Jupiter’s thermosphere, the thin outer layer starting at pressures around a millionth of a bar, is hundreds of degrees hotter than models predict based on solar heating alone. This “energy crisis” has been a nagging problem in planetary science for decades.
Several explanations have been proposed. One is that acoustic or gravity waves propagating upward from the turbulent lower atmosphere deposit their energy in the thermosphere. Another is that the enormous amount of energy dumped into the polar auroral regions by Jupiter’s interaction with its magnetosphere gets redistributed globally.17The Astrophysical Journal Letters. Temperatures of Jupiter’s Upper Atmosphere: The Role of the Planetary Magnetic Field The auroral heating is certainly strong enough in total, but three-dimensional models of Jupiter’s upper atmosphere show that getting that energy from the poles to the equator is not straightforward. Jupiter’s fast rotation creates strong wind patterns that tend to trap heat near the poles rather than spreading it evenly.18Journal of Geophysical Research: Planets. Jupiter Thermospheric General Circulation Model (JTGCM): Global structure and dynamics driven by auroral and Joule heating
The thermosphere is, in one sense, the only part of Jupiter’s atmosphere that deserves the word “thin.” At pressures below a microbar, the gas is genuinely rarefied, more vacuum than atmosphere. But even this thin layer extends hundreds of kilometers above the cloud deck because Jupiter’s gravity, while strong, is spread over such a vast radius that the atmosphere can puff up to great heights before thinning to near-nothing.
How Jupiter Compares to the Other Gas Giants
All four outer planets in our solar system lack solid surfaces, so the “thick or thin” question applies to each of them. But the answers differ in interesting ways. Saturn’s atmosphere, as mentioned earlier, has jet streams extending about three times deeper than Jupiter’s, likely because Saturn’s lower mass and weaker magnetic field allow organized flows to penetrate further before being damped.9Geophysical Research Letters. Depth Dependent Dynamics Explain the Equatorial Jet Difference Between Jupiter and Saturn Uranus and Neptune are classified as “ice giants” rather than gas giants because they contain a higher proportion of water, ammonia, and methane ices relative to hydrogen. Their atmospheres are thinner in the sense that the hydrogen-helium envelope makes up a smaller fraction of the planet, but they still have no solid surfaces and still feature active weather extending deep below their cloud tops.
Jupiter remains the most massive and most studied of the group. Its equatorial radius of roughly 71,492 kilometers means the gaseous envelope alone is more than eleven times wider than Earth.1arXiv. Giant planet interiors and atmospheres Even if you restrict your definition of “atmosphere” to the wind-bearing layer above the metallic hydrogen transition, you are still talking about a shell of gas thousands of kilometers deep. By any reasonable measure, Jupiter’s atmosphere is one of the thickest envelopes of any known planet, not because it is unusually bloated for a gas giant, but because a gas giant’s atmosphere is, by definition, most of the planet itself.