The researchers asked whether a wavy band appearing around Saturn's south pole was a coherent polygonal atmospheric wave, how it moved, and whether it resembled the planet's long-lived northern hexagon.
The research question and why it matters
The researchers asked whether a wavy band appearing around Saturn's south pole was a coherent polygonal atmospheric wave, how it moved, and whether it resembled the planet's long-lived northern hexagon.
Voyager first imaged Saturn's northern polar region in 1980–1981, and the north-polar hexagon has remained observable for more than 40 years. Cassini monitored Saturn from 2004 to 2017 without revealing a comparable long-lived southern polygon. Laboratory rotating-fluid experiments and atmospheric models have shown that fast jets can support polygonal waves, but they have not yet explained why Saturn's two poles would display different side counts and stability.
What researchers found
By 2025 the band formed ten recognizable sides between roughly 58°S and 63°S. The pattern drifted eastward at about 2.5 meters per second relative to Saturn's radio-rotation frame, far slower than the approximately 116-meter-per-second jet centered near 60.5°S. Individual vertices also oscillated in longitude with an average period near 32 days and amplitudes of 4.6° to 8.4°. Its slightly different position in different filters indicates that the wave extends vertically through more than one atmospheric level.
Key results from the tested systems
sides tracked
The vertices became clearest in 2025 Hubble images after weaker indications in 2023 and 2024.
latitude band
The atmospheric wave encircles the south-polar region inside a strong eastward jet.
eastward pattern drift
The surrounding jet peaked near 116 m/s, showing that the wave pattern and moving gas are not the same speed.
average vertex oscillation period
Individual vertices shifted by roughly 4.6° to 8.4° around the mean drift.
How the research worked
The team remapped full-rotation images of Saturn's south-polar region into polar projections, identified brightness vertices in several filters, and tracked their longitude over time. Different Hubble filters sampled different atmospheric levels. Ground-based images submitted through the Planetary Virtual Observatory Laboratory helped identify the feature, while Hubble's sharper annual OPAL observations traced it back to 2023. The researchers compared the pattern's drift with Saturn's System III radio-rotation frame and with wind speeds in the surrounding jet.
How to interpret this design
The design determines what kind of conclusion the evidence can support. Direct measurement strengthens the reported observation, while generalization beyond the tested subjects, material, place or conditions requires additional evidence.
Astronomers cannot manipulate the object experimentally, so the conclusion comes from measured light, motion or other signals interpreted through physical models. Alternative explanations and instrument limits therefore matter.
What strengthens or limits the finding?
Independent ground-based observations first revealed an undulating band, and repeated high-resolution Hubble observations traced ten vertices across multiple years and wavelengths. The geometry and motion are observationally supported, while the physical explanation is still a model and the short time series cannot establish long-term stability.
The result is meaningfully informative, but identifiable limitations could alter the size, reach or causal interpretation of the finding.
Funding and disclosure context
The recorded funding source is: Basque Government research group IT1742-22 and Spanish grant PID2023-149055NB-C31 were among the support listed in the paper; Hubble observations were obtained through the NASA/ESA Outer Planet Atmospheres Legacy program. The complete funder list is available in the primary paper.. The recorded conflict information is: The authors declared no competing interests. Funding or a disclosed relationship does not by itself invalidate a result, but it is relevant when judging design choices, analysis and the need for independent replication.
What it means
Saturn now offers two natural laboratories for polygonal jet-stream behavior: a northern hexagon that has persisted for more than four decades and a southern decagon that appears to be evolving. Continued observations may show how large atmospheric waves form, become trapped in jets and either stabilize or disappear on rapidly rotating giant planets.
Deeper analysis
A wave can move more slowly than the wind carrying it
The roughly 2.5-meter-per-second drift describes the progression of the geometric pattern in Saturn's rotation frame, not the speed of the gas. The local jet moves about 46 times faster. That separation between pattern speed and fluid speed is a hallmark of large atmospheric waves.
Several filters add a vertical dimension
Hubble filters do not all see the same pressure level. Small shifts in the decagon's apparent position across wavelengths therefore suggest a structure extending through multiple layers, rather than a drawing confined to one cloud deck.
The observing gap matters
Cassini saw no durable southern polygon before its mission ended in 2017, and the south pole then became harder to observe. Finding the shape in 2023 imagery constrains the timeline but leaves several years in which it could have emerged unseen.
The difference between detection and explanation
Repeated images support the existence, shape and motion of the decagon. Calling it a vertically trapped Rossby wave is a physically motivated hypothesis. A successful model that produces the observed side count, drift and oscillation is still needed before that mechanism can be treated as established.
What it does NOT prove
- It does not show that Saturn has a solid 10-sided object or wall. The decagon is a moving brightness and wind pattern in the atmosphere.
- It does not prove that the feature formed in 2023. That is the earliest year in which the team could trace it in the available Hubble sequence.
- It does not establish that the decagon will persist for decades like the northern hexagon.
- It does not confirm the proposed Rossby-wave mechanism; that interpretation still needs dynamical modeling and more observations.
- It does not show that every apparent vertex has identical strength at every altitude or date.
Important limitations
- The well-resolved record covers only a few Earth years, too short to measure longevity on a planet whose seasons last more than seven Earth years.
- Saturn's viewing geometry and seasonal illumination limited observations of the south pole, leaving a gap between Cassini's mission and the first Hubble hints.
- Cloud brightness is an indirect tracer of atmospheric motion and can vary with altitude, chemistry and illumination.
- The apparent latitude and contrast shift among filters because they probe different atmospheric levels, complicating a single geometric boundary.
- Ground-based images have lower and variable resolution, while Hubble observations occur at discrete intervals rather than continuously.
- A quasi-geostrophic Rossby wave is a plausible interpretation, but the study does not yet reproduce the decagon's formation and evolution in a validated atmospheric model.
How this fits with previous research
Voyager first imaged Saturn's northern polar region in 1980–1981, and the north-polar hexagon has remained observable for more than 40 years. Cassini monitored Saturn from 2004 to 2017 without revealing a comparable long-lived southern polygon. Laboratory rotating-fluid experiments and atmospheric models have shown that fast jets can support polygonal waves, but they have not yet explained why Saturn's two poles would display different side counts and stability.
Questions still unanswered
- When did the decagon actually form, and was a specific storm or jet instability the trigger?
- Will its drift, 32-day vertex oscillation and side count remain stable through Saturn's changing seasons?
- How deep does the wave extend below the visible cloud and haze layers?
- Can three-dimensional circulation models reproduce ten sides, the measured drift and the surrounding jet simultaneously?
- Why has Saturn's northern pattern remained nearly stationary while the southern feature moves and evolves?
Relevant U.S. government resources
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Hubble tracked a developing 10-sided wave around Saturn's south pole
This review was developed from the source record below and, when separately available, the primary paper or government report. The summary and analysis on this page are original editorial writing.
- Source organization
- NASA
- Source type
- U.S. government
- Authors
- Agustín Sánchez-Lavega, Amy A. Simon, Michael H. Wong, Leigh N. Fletcher, Arrate Antuñano, Ricardo Hueso, Peio Iñurrigarro, Aida Flix-Bellmunt, Arnau Miró, Enrique García-Melendo, Trevor Barry, Jean-Paul Oger, Glenn S. Orton and Itziar Garate-Lopez
- Journal / report
- Science Advances
- Publication date
- September 2, 2026
- DOI
- 10.1126/sciadv.aee4251
- PMID
- Not available
- Institution
- University of the Basque Country-led international collaboration with NASA Goddard Space Flight Center, University of California Berkeley, University of Leicester, Universitat Politècnica de Catalunya, NASA Jet Propulsion Laboratory and participating ground-based observers
- Funding
- Basque Government research group IT1742-22 and Spanish grant PID2023-149055NB-C31 were among the support listed in the paper; Hubble observations were obtained through the NASA/ESA Outer Planet Atmospheres Legacy program. The complete funder list is available in the primary paper.
- Conflicts
- The authors declared no competing interests
- Open access
- Yes
- Reuse approach
- Facts summarized in original language from NASA, the open peer-reviewed paper record and the official conference abstract; no source wording, photographs, telescope images, figures, maps, tables or code reproduced.
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