TL;DR: Hubble watched a blue 10-sided jet wave form around Saturn's south pole.

A giant blue decagon encircling Saturn's south pole emerged in Hubble Space Telescope views from 2023 to 2025, the first large, regular-sided southern pattern ever recorded there, according to the UC Berkeley Space Sciences Lab.

The finding was reported Sept. 2, 2026, in a paper in Science Advances by researchers from the UC Berkeley Space Sciences Laboratory, NASA's Goddard Space Flight Center and the University of the Basque Country, according to the UC Berkeley Space Sciences Lab. The team tracked the ten-sided jet-stream wave by reviewing Hubble images extending back to 2023. Co-author Michael Wong, a Space Sciences Laboratory researcher, said the pattern was absent a few years earlier, underscoring the value of repeated looks at the outer planets.

That rapid appearance contrasts with Saturn's northern hexagon. The six-sided northern polar jet was first seen in 1980 and has persisted on every subsequent look for more than 40 years, according to NASA Science. The new southern feature, by contrast, appears to be strengthening, offering a rare chance to observe development of a planetary-scale wave.

A southern counterpart at last

The northern hexagon surrounds Saturn's north pole and has long puzzled researchers. Laboratory work has reproduced a six-sided shape by rotating a circular tank of fluid, yet the cause of the Saturn version and its slow shift from blue to gold remain under debate, according to the UC Berkeley Space Sciences Lab.

After that northern discovery, scientists looked for a southern equivalent and found none. In 2004, NASA's Cassini spacecraft photographed the full southern hemisphere and did not record a hexagon, according to the UC Berkeley Space Sciences Lab. It did record short-lived polygonal-looking disturbances in the east-to-west jet band at 60.5°S, but that texture faded within days and did not return before Cassini finished with a deliberate entry into Saturn's atmosphere in 2017.

The new decagon sits in southern jet flow and stretches across multiple atmospheric levels, indicating a vertically extended structure rather than a thin cloud marking, according to NASA Science. Its apparent latitude changes slightly with observing wavelength because separate filters sample separate heights.

How Hubble caught the emergence

The discovery relied on Hubble's Outer Planet Atmospheres Legacy program, known as OPAL, which images Jupiter, Saturn, Uranus and Neptune each year with Wide Field Camera 3, according to the UC Berkeley Space Sciences Lab. Saturn coverage under OPAL began in 2018 after Cassini ended.

OPAL grew from gaps in earlier coverage. In 2009, Wong was a visiting scientist at the Space Telescope Science Institute during calibration of the newly installed Wide Field Camera 3, according to the UC Berkeley Space Sciences Lab. That year a major impact scar appeared on Jupiter, and Wong used the new camera to record what became its first science images of Jupiter. No Jupiter images followed in 2011 and 2013, and those interruptions prompted OPAL principal investigator Amy Simon, a planetary scientist at NASA Goddard, to propose annual surveys of all four giant planets.

The yearly cadence has since documented other slow changes. In 2021, Wong, Simon and Glenn Orton, a senior research scientist at NASA's Jet Propulsion Laboratory, reported faster winds in Jupiter's Great Red Spot, according to the UC Berkeley Space Sciences Lab. In 2023 the group reported brightening of Uranus' northern polar hood, and in July 2026 it published the full life cycle of a dark cyclonic spot on Neptune.

For Saturn, the program preserved views from October 2023, August 2024 and August-September 2025 that together show the decagon sharpening. The Science Advances paper reports that 2023 and 2024 frames showed sides and corners with weaker brightness contrast, consistent with an evolving system.

Ground telescopes spotted the first hint

The first modern hint did not come from Hubble alone. Agustín Sánchez-Lavega, the study lead author at the University of the Basque Country, works with ground-based contributions through the Planetary Virtual Observatory Laboratory, called PVOL, according to the UC Berkeley Space Sciences Lab. A 2024 image sent to that archive showed a wavy disturbance resembling the brief pattern Cassini had recorded about two decades earlier.

Sánchez-Lavega then contacted the OPAL team to inspect sharper Hubble views of the southern hemisphere. When the 2024 and 2025 Hubble frames were remapped into polar projections, a ten-sided outline stood out near 63°S, according to the UC Berkeley Space Sciences Lab.

NASA Science reports that Sánchez-Lavega examined those ground images with amateur astronomers Trevor Barry and Jean-Paul Oger. They noticed a faint undulating band near the southern pole in 2024, with stronger ground-based hints in 2025. Hubble then supplied continuous sharpness across full rotations without blurring by Earth's atmosphere.

Seasonal geometry helped. Saturn's tilt had hidden the south polar region from Earth-based viewing after mid-2012, and the zone only became accessible again around 2023, according to the Science Advances paper. Sánchez-Lavega said researchers had sought a southern match for the northern hexagon in Hubble data since 1990, while Cassini's 2004-2017 orbital tour showed no durable southern polygon, according to NASA Science.

Size, motion and vertical structure

The paper places the 2025 decagon between planetographic latitudes of about 58°S and 63°S. Three of its ten corners and sides looked very prominent in August and September 2025, four were moderately prominent and three were weakly defined, while ground telescopes also recorded the pattern in 2025, according to the Science Advances paper.

In red filters at 631, 727, 763 and 937 nanometers, the wave center lay at 63°S, plus or minus 0.4 degrees. In the strong methane absorption band at 889 nanometers, which samples higher tropospheric aerosols, the center appeared closer to the equator at 60.5°S, plus or minus 0.4 degrees, according to the Science Advances paper. That offset supports a three-dimensional shape.

The wave number is 10, with an average east-west wavelength of 16,782 kilometers, plus or minus 1,100 kilometers. Its crests and troughs trace a sine-like latitude oscillation with a peak-to-peak range of 2.7 degrees, plus or minus 0.3 degrees, equal to 2,645 kilometers, according to the Science Advances paper.

The visible blue portion lies in the upper troposphere, where associated winds reach about 400 kilometers per hour, according to the UC Berkeley Space Sciences Lab. The 10-sided drift moves eastward at only 2.5 meters per second, far slower than the 116-meter-per-second zonal jet at 60.5°S, while the longitudes of its corners swing back and forth with a 32-day period and amplitudes of 4.6 to 8.4 degrees, according to the Science Advances paper.

A fainter decagonal undulation also appears outside the main wave: in a dark belt centered at 53°S in 2023 and 2024 and at 58°S in 2025 at 763 nanometers, plus a white band at 58.8°S in the 889-nanometer methane filter in 2025, according to the Science Advances paper. Those bands are about 2 to 3 degrees wide, or roughly 2,000 to 3,000 kilometers.

Why it may have formed

The makeup of the blue aerosols remains unknown, as does the deeper extension of the wave beneath the observed levels, according to the UC Berkeley Space Sciences Lab. Sánchez-Lavega built a shallow-water equation model showing that a ten-sided pattern can arise in a turbulent fluid, but the precise Saturn mechanism is unresolved.

One possible trigger sits immediately to the north. The authors note a compact anticyclonic vortex near 55°S that was first seen in 2023 and darkened sharply in 2025 shortly before the decagon became distinct, according to the UC Berkeley Space Sciences Lab. The Science Advances abstract describes two modeled possibilities: a spatially periodic disturbance at the jet peak, or forcing by that dark anticyclone just north of the wave.

The paper interprets the decagon as a large meandering wave held in height and confined sideways by curvature of the dominant jet. Simon said the central puzzle is timing — why such a pattern would appear now after decades without a southern example — according to NASA Science.

For comparison, the northern hexagon is centered near 78.5°N planetographic latitude, was found in Voyager flybys in 1980-1981 and has lasted more than 44 years, according to the Science Advances paper. It overlies an eastward jet near 100 meters per second yet stays almost fixed in longitude relative to Saturn's System III radio rotation period, and its thermal signature reaches above the upper clouds into the stratosphere. The southern jets at 60°S and 73.6°S are similarly long-lived, which had made a southern wave seem plausible even though none had been confirmed.

What comes next

The authors call for continued Hubble monitoring, new observations with NASA's James Webb Space Telescope and further numerical modeling to determine how the decagon arose, how long it endures and how closely it resembles the northern hexagon, according to NASA Science.

The immediate question is stability. The team intends to keep observing Saturn to learn whether the ten-sided pattern settles into a durable arrangement like the northern six-sided wave or keeps changing, according to NASA Science. Later work may also clarify what the wave reveals about circulation on giant planets, including parallels to terrestrial atmospheric dynamics.

Hubble's longevity makes that watch possible. The telescope has operated for more than three decades as a cooperative project of NASA and ESA, with Goddard managing operations in Greenbelt, Maryland, according to NASA Science. Wong said many OPAL findings depend not on a single snapshot but on years of repeated measurements.

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