Scientists have spent decades trying to figure out how much oxygen Jupiter contains. The answer matters because it reveals where and how the solar giant formed 4.5 billion years ago. A new study combining advanced computer modeling has finally cracked the case: Jupiter holds 1.0 to 1.5 times the Sun’s oxygen levels—five times higher than previous estimates suggested.
The discovery resolves a major conflict in planetary science and raises new questions about why Jupiter accumulated so much carbon relative to oxygen during its formation.
Water carries most of Jupiter’s oxygen, but measuring water in the planet’s deep atmosphere presents massive challenges. Water condenses into clouds and gets churned around by violent atmospheric currents. Temperatures soar above 1,000 degrees Fahrenheit hundreds of miles below the cloud tops, where pressures reach hundreds of times Earth’s surface pressure. No probe can survive down there long enough to take accurate readings.
Scientists found a workaround: carbon monoxide. At Jupiter’s extreme depths, chemistry strongly favors methane over carbon monoxide. But as gas bubbles upward toward cooler regions, chemical reactions slow down dramatically. The carbon monoxide gets “frozen” in place chemically, preserved as it rises to altitudes where telescopes can detect it. By measuring upper-atmosphere carbon monoxide levels, researchers can calculate the oxygen abundance far below.
The method works in principle. In practice, it demands precise knowledge of two things: the exact chemical reactions converting carbon monoxide to methane, and how vigorously Jupiter’s atmosphere mixes vertically. Previous studies got both wrong.
In 1989, Japanese scientist Yoshinori Hidaka measured how methanol breaks apart when struck by hydrogen atoms. The reaction produces methane and water. Hidaka published his results, and the reaction entered scientific databases. Then someone made a data entry error. The NIST chemistry database listed the reaction rate as 100 times faster than Hidaka actually measured. Some scientists used the wrong value. Others excluded the reaction entirely, arguing it seemed too fast. Still others used the correct original value but disagreed about whether to include it at all.
The confusion mattered enormously. The Hidaka reaction significantly accelerates carbon monoxide’s conversion to methane in Jupiter’s depths. Include it, and less carbon monoxide reaches the upper atmosphere. Exclude it, and predictions don’t match observations. Use the wrong rate, and everything falls apart.
The JPL team verified the correct reaction rate using high-level quantum chemistry calculations. Multiple independent theoretical studies confirmed Hidaka’s original measurements were accurate. The reaction belongs in Jupiter models, and it substantially changes the results.
Previous one-dimensional models treated Jupiter’s atmosphere like a simple column of gas with a single “mixing strength” parameter. Real atmospheres don’t work that way. Water condenses, releasing heat that drives circulation. Winds blow horizontally and vertically. Turbulent eddies stir the gas at all scales.
The research team built a two-dimensional simulation of Jupiter’s atmosphere using the SNAP hydrodynamic code. The model creates a vertical slice through the planet, tracking how water vapor, carbon monoxide, and other chemicals move and react over 1,000 simulated days. Unlike simplified models, SNAP calculates the actual physics of cloud formation, convection, and atmospheric mixing.
Separately, the team ran detailed one-dimensional chemistry calculations using EPACRIS software and an automated chemical network containing 1,968 reactions among 89 molecular species. The network came from the Reaction Mechanism Generator, an algorithm that systematically identifies important reactions rather than relying on researchers to manually compile lists.
The two completely independent approaches—detailed chemistry with simplified physics versus simplified chemistry with detailed physics—arrived at the same answer. Jupiter contains 1.0 to 1.5 times the solar oxygen abundance. When different methods point to identical conclusions, the result gains credibility.
The finding aligns with recent measurements from NASA’s Juno spacecraft orbiting Jupiter. Juno’s microwave radiometer detects water vapor deep below the cloud tops. Early Juno results suggested oxygen abundances between 1.5 and 8.3 times solar, with large uncertainties. The new value sits at the lower end of Juno’s range, suggesting Jupiter’s oxygen enrichment is modest rather than extreme.
The Galileo probe that plunged into Jupiter in 1995 established that the planet contains four times more carbon than the Sun, relative to hydrogen. Scientists accepted this measurement as solid. The new oxygen measurement creates a surprising picture. Jupiter’s carbon-to-oxygen ratio reaches approximately 2.9—more than five times the Sun’s ratio of 0.55. The planet accumulated far more carbon relative to oxygen than existed in the average solar nebula.
The answer involves where Jupiter formed and what materials were available. At different distances from the infant Sun, different substances froze out of the gas. Carbon existed in carbon monoxide ice, methane ice, and complex organic compounds. Oxygen came primarily from water ice. Temperature determined which ices could exist at which locations.
Jupiter’s high carbon-to-oxygen ratio indicates the planet formed in a region unusually rich in carbon-bearing ices compared to water ice. Either Jupiter assembled farther from the Sun than expected, then migrated inward, or carbon-rich particles somehow concentrated in Jupiter’s formation zone through drift and sorting processes in the protoplanetary disk.
Recent studies of Kuiper Belt objects like Pluto independently suggest the outer solar system had higher carbon-to-oxygen ratios than previously believed. Jupiter’s composition provides powerful evidence supporting this view.
The team also developed a new method for calculating atmospheric mixing strength directly from physics rather than guessing. Traditional models assume a value for the “eddy diffusion coefficient” describing how vigorously atmospheres mix. The SNAP simulations let researchers derive this coefficient from the actual fluid dynamics as the model approached steady state.
The physics-based mixing strength came out to 3×10⁶ to 5×10⁷ cm²/s, lower than the commonly assumed value of 10⁸ cm²/s but consistent with other recent Jupiter observations. The method works for any planet with a thick atmosphere, making it valuable for studying distant exoplanets where direct measurements remain impossible.
Jupiter has been observed through telescopes for over 400 years, since Galileo first spotted its four largest moons in 1610. Spacecraft have visited since the 1970s. We crashed a probe into its atmosphere and maintained an orbiter studying it for years. Yet fundamental questions about something as basic as how much oxygen it contains remained unresolved until now.
The researchers identified no single rate-limiting chemical reaction controlling carbon monoxide’s conversion to methane. Previous studies often assumed one specific reaction dominated, simplifying calculations. The reality proves more complex. Both the Hidaka reaction and methanol’s thermal decomposition contribute significantly to methane formation. Multiple reactions proceed at comparable rates, and slight variations in temperature, pressure, or composition can shift which pathways matter most.
The direct approach taken by the team—computing chemical timescales from the eigenmodes of the full reaction network rather than focusing on individual reactions—provides more accurate predictions. The method considers all relevant reactions simultaneously, capturing the nonlinear interplay among competing chemical pathways.
The carbon monoxide measurements used to constrain these models come from observations by astronomers Bruno Bézard and colleagues in 2002, later refined by Gordon Bjoraker’s team in 2018. They detected carbon monoxide in Jupiter’s upper troposphere at mixing ratios around 1 to 3 parts per billion. The models needed to reproduce these measurements while accounting for all the chemistry and atmospheric mixing happening between the deep interior and the observable upper layers.
A 2023 study by Thibault Cavalié and colleagues had reported subsolar oxygen abundance around 0.3 times the Sun’s value. That paper used an updated chemical network but excluded the Hidaka reaction and assumed strong atmospheric mixing. The new work shows that including the Hidaka reaction and deriving mixing strength from physics rather than assuming it leads to oxygen abundances five times higher.
The difference between 0.3 and 1.5 times solar oxygen abundance carries major consequences for understanding Jupiter’s formation. Subsolar oxygen would suggest Jupiter formed from material depleted in water ice, perhaps indicating formation inside the “snow line” where water remains gaseous. Supersolar oxygen would point to formation beyond the snow line with efficient accumulation of water ice. The new modest supersolar value—barely enriched compared to the Sun—suggests Jupiter formed just beyond the snow line or accumulated a mix of water-poor and water-rich materials.
The simulations ran for the equivalent of 1,000 Jovian days, far longer than previous attempts. Extended run times proved critical for reaching true steady state rather than temporary quasi-equilibrium. Earlier studies that ran shorter simulations derived higher oxygen abundances because the models hadn’t fully converged. The difference between running 200 days versus 1,000 days shifted the inferred oxygen content by a factor of nearly two.
Each simulation tracked the carbon monoxide distribution until the rate of change dropped below 10⁻¹⁶—essentially machine precision zero. At that point, chemical production and loss balanced hydrodynamic transport so precisely that the average carbon monoxide profile stopped evolving. Only then could researchers extract meaningful constraints on oxygen abundance.
The research team tested oxygen abundances ranging from 0.3 to 2.3 times solar. The 2.3 times solar case produced too much carbon monoxide compared to observations, even with slow atmospheric mixing. The 0.3 times solar case required unrealistically fast mixing to produce enough carbon monoxide. Only the 1.0 to 1.5 times solar range matched observations with physically plausible mixing rates.
Temperature and pressure determine which chemical reactions proceed quickly versus slowly. In Jupiter’s upper troposphere, temperatures around 150 Kelvin freeze most chemistry. Carbon monoxide arriving from below stays locked in that form because reactions converting it to methane take millions of years at those temperatures. Deeper down, at 1,000 Kelvin and 500 bars pressure, the conversion happens in days. The transition between these regimes—called the quench point—occurs around 500 bars and 1,050 Kelvin for the conditions modeled.
Water clouds form between 5 and 10 bars pressure depending on oxygen abundance. The clouds release latent heat when water vapor condenses, which drives convection. The convection mixes carbon monoxide upward from below the clouds. Cloud microphysics and convection couple in complex ways that one-dimensional models cannot capture. The two-dimensional SNAP simulations explicitly resolved cloud formation, convective updrafts and downdrafts, and the resulting distribution of chemical tracers.
Negative eddy diffusion coefficients appeared in some regions of the SNAP simulations—a result impossible in traditional one-dimensional models but physically meaningful. Negative values indicate that horizontal motions actually reduce vertical mixing in those areas, creating stable layers resistant to vertical transport. The phenomenon occurs when horizontal winds correlate with tracer concentrations in ways that oppose vertical gradients. Three-dimensional simulations show similar behavior.
The automated Reaction Mechanism Generator proved less sensitive to individual reaction uncertainties than manually constructed networks. Earlier hand-built networks sometimes changed their predictions dramatically when a single reaction was added, removed, or updated. The RMG network, containing nearly 2,000 reactions, showed more robust behavior. Even changing the Hidaka reaction rate by an order of magnitude shifted predicted carbon monoxide levels by less than a factor of two.
The carbon-to-oxygen ratio of 2.9 inferred for Jupiter exceeds recent estimates of the protosolar value, which range from 0.55 to 0.73. The discrepancy means Jupiter’s feeding zone in the protoplanetary disk must have been enriched in carbon or depleted in oxygen compared to the average composition. Several mechanisms could produce such fractionation. Carbon-rich dust grains might have drifted inward through the disk faster than water ice grains due to size or composition differences. Alternatively, Jupiter could have preferentially accreted carbon-rich planetesimals while most water ice remained in smaller bodies that Jupiter’s gravity failed to capture efficiently.
The methodology developed for Jupiter applies directly to Uranus and Neptune, the ice giant planets that remain poorly explored. Only Voyager 2 has visited them, conducting brief flybys in the 1980s. No orbiter has ever studied either planet in detail. Uranus and Neptune likely have even more complex atmospheric chemistry than Jupiter because they contain larger fractions of heavy elements. Understanding their oxygen abundances would reveal whether they formed in situ at their current distances from the Sun or migrated outward from formation zones closer in.
Exoplanet atmospheres present similar challenges. Astronomers have detected thousands of planets orbiting other stars, but characterizing their compositions remains difficult. Telescopes can measure some atmospheric constituents by analyzing starlight filtered through planetary atmospheres during transits. Converting those observations into elemental abundances requires detailed models of atmospheric chemistry and dynamics—exactly the type of coupled modeling demonstrated in the Jupiter study.
The James Webb Space Telescope has begun observing exoplanet atmospheres with unprecedented sensitivity. Water, methane, carbon monoxide, and carbon dioxide have been detected in multiple systems. Interpreting these detections to infer oxygen and carbon abundances demands models that properly account for both chemistry and atmospheric mixing. The techniques validated on Jupiter—where we can check predictions against in situ measurements—provide the foundation for analyzing alien worlds where we’ll never send probes.
Jupiter’s surprisingly carbon-rich composition suggests that similar processes might operate around other stars. Some exoplanets show carbon-to-oxygen ratios greater than one, meaning they contain more carbon than oxygen. Others appear oxygen-rich. Understanding what controls these ratios has become a major research focus. Jupiter provides our best laboratory for testing theories because we can study it in far greater detail than any exoplanet.
The Juno mission continues to refine measurements of Jupiter’s deep atmosphere. Each orbit provides new data about water distribution, which translates to oxygen abundance measurements. The spacecraft’s microwave instrument penetrates hundreds of kilometers below the cloud tops, reaching depths inaccessible to optical telescopes. Combining Juno’s growing dataset with the improved modeling techniques from the new study should progressively narrow the uncertainties.
Future missions to Jupiter’s moons—Europa, Ganymede, and Callisto—will carry instruments capable of studying Jupiter’s atmosphere from orbit. The Europa Clipper mission launching in 2024 and the European Space Agency’s JUICE mission will both conduct Jupiter observations while investigating the moons. Additional atmospheric data from different viewing geometries and wavelengths will help constrain composition models.
The research was carried out at NASA’s Jet Propulsion Laboratory and the California Institute of Technology. The team included Jeehyun Yang, Ali Hyder, Renyu Hu, and Jonathan Lunine. They published their findings in January 2026 in The Planetary Science Journal. The work combines expertise in atmospheric chemistry, fluid dynamics, planetary formation theory, and observational astronomy—a truly interdisciplinary effort.
Giant planet formation remains one of the outstanding problems in planetary science. Jupiter formed within a few million years of the solar system’s birth, fast enough to capture massive amounts of hydrogen and helium before the Sun’s radiation dispersed the gas. The planet’s composition preserves information about that formative era, a cosmic time capsule recording conditions in the infant solar system. Every new measurement refines our understanding of how planets form from disks of gas and dust around young stars. Jupiter’s oxygen and carbon abundances constrain where in the disk the planet formed, what materials were available, and how efficiently the growing planet accumulated different substances. These same processes occur around other stars, shaping the diversity of planetary systems we now know populate the galaxy.
Source:
Yang, J., Hyder, A., Hu, R., & Lunine, J. I. (2026). Coupled 1D Chemical Kinetic Transport and 2D Hydrodynamic Modeling Supports a Modest 1–1.5× Supersolar Oxygen Abundance in Jupiter’s Atmosphere. The Planetary Science Journal, 7(2). https://doi.org/10.3847/PSJ/ae28d5
