Each side of the southern decagon spans roughly 16,800 kilometers — a few thousand miles longer than Earth’s entire diameter. A nearby jet stream races at 116 meters per second, close to 260 miles per hour, yet the polygon itself drifts at just 2.5 meters per second, under 6 miles per hour. The contrast between the violent winds and the slow, steady shape is one of the details researchers find most puzzling.
How the Saturn Decagon Was Found
For decades, scientists searched the southern hemisphere for a counterpart to the northern hexagon without success. Saturn’s axial tilt kept the south pole poorly positioned for Earth-based viewing across long stretches of its 29-year orbit, leaving the region in shadow or at an awkward angle for most major observing campaigns.
The first hints came not from flagship observatories but from ground-based observations, including some by amateur astronomers watching Saturn’s southern cloud bands. As the images piled up, researchers noticed persistent oddities. Digging through archival Hubble data, they traced the pattern back to images taken in 2023. By 2025, the 10 vertices had sharpened enough to confirm the feature as a genuine polygonal structure rather than a transient cloud arrangement.
Waves Trapped by Jet Streams
Saturn has no solid surface. Descending through its atmosphere, pressure and density would rise steadily but never deliver anything resembling ground. That makes the polar polygons especially striking: they are patterns sculpted entirely from moving gas.
The leading explanation, developed after the northern hexagon’s discovery, treats the shapes as atmospheric waves pinned in place by powerful jet streams. Like ocean swells striking a coastline, waves of gas encounter the jet stream’s boundary and bend into standing patterns. The geometry depends on how many times a current coils around the planet before closing on itself — six coils produce a hexagon, ten coils a decagon.
Saturn’s rapid rotation, exact wind speeds, and variations in the currents all likely contribute to which geometry emerges. A current that wraps six times can settle into a hexagon; one that wraps ten times can settle into a decagon. This framework explains how a fluid atmosphere without any solid structure can produce something that looks, from orbit, like a gigantic drawn polygon.
Questions the Decagon Raises
The discovery reframes several open questions about Saturn’s polar meteorology. Researchers still do not know how deep these geometric figures extend into the atmosphere, how long the new decagon might persist, or whether its appearance is tied to Saturn’s seasons. Most fundamentally, no one knows what triggered its formation in the first place.
The timing is suggestive. The southern decagon emerged as Saturn’s south pole tilted back toward sunlight after years of poor viewing geometry. If the structure is seasonal, it may strengthen, fade, or vanish as the planet continues its slow orbital march. If it is not, its persistence would point to deeper atmospheric dynamics independent of solar heating.
Comparing the two poles directly is now possible for the first time. The northern hexagon has held steady for at least 44 years, surviving seasonal shifts and massive storms. Whether the southern decagon shows similar endurance will become clear only with continued monitoring.
What Happens Next
Researchers plan to track the Saturn decagon’s evolution using both the Hubble Space Telescope and the James Webb Space Telescope, combining visible-light and infrared observations to probe different depths of the atmosphere. More advanced atmospheric models will attempt to reconstruct the conditions capable of spawning a 10-sided wave pattern, testing whether the jet-stream-coil hypothesis holds under closer scrutiny.
Watch for follow-up results from the Hubble monitoring campaign within the next year, and for early James Webb infrared data that could reveal whether the decagon extends deeper than the visible cloud tops. If the structure changes with Saturn’s seasons, the coming years — as the southern hemisphere moves through its summer — should show it most clearly.
— Priya Nair, science desk, AXO News