Hubble Telescope Discovers Massive Decagon Wave at Saturn's South Pole

Astronomers using the Hubble Space Telescope have discovered a massive, 10-sided atmospheric wave pattern encircling Saturn’s south pole. The newly confirmed decagon, which spans roughly 104,250 miles across, provides planetary scientists with an unprecedented look at a giant polar vortex actively forming and strengthening in real time.

Saturn continues to rewrite planetary meteorology textbooks. Researchers analyzing high-resolution data from NASA’s Hubble Space Telescope have confirmed the existence of a colossal geometric wave at the ringed giant’s southern pole. The structure, dubbed a decagon, spans 167,820 kilometers across, dwarfing the planet’s famous northern hexagon. While atmospheric jets are common on spinning gas giants, the persistence of sharp, straight-edged polygonal boundaries has long stood out as a peculiar quirk unique to Saturn.

Ground-Based Hints and Hubble’s Space-Based Archive

The discovery emerged from a collaborative effort between professional researchers and amateur observers. Because of Saturn’s 29.5-year orbit and axial tilt, its southern hemisphere remained tilted away from Earth’s direct line of sight between 2012 and 2023. As seasonal shifts brought the south pole back into view, ground-based astronomers caught their first glimpses of an anomaly.

Hubble Telescope Discovers Massive Decagon Wave at Saturn's South Pole — Photo: earthsky.org

Lead author Agustín Sánchez-Lavega, a planetary scientist at the University of the Basque Country in Spain, first noticed a faint, undulating band in southern polar images submitted to Planetary Virtual Observatory Laboratory in 2024. Amateur astronomers Trevor Barry and Jean-Paul Oger contributed key observations, which grew sharper in ground images captured throughout 2025 at facilities like the Calar Alto Observatory in Spain.

To verify the phenomenon free from atmospheric blurring, the international team turned to archival data from Hubble’s Outer Planet Atmospheres Legacy (OPAL) program. Those space-based observations confirmed subtle hints of the decagon beginning to take shape as early as 2023.

Multi-Layered Dynamics and High-Speed Jet Streams

The decagon sits embedded within a high-speed southern jet stream located around 60 degrees south latitude, featuring winds clocked at 250 mph (400 to 420 km/h). Each of its 10 geometric sides measures approximately 10,425 miles across, and the entire wave rotates at a gradual pace, taking roughly 800 Earth days to complete a single circuit around the planet.

However, the angular geometry of the jet stream rather than a smooth circle points to deeper atmospheric mechanics.

Hubble’s multi-wavelength imaging revealed that the decagon is not just a superficial cloud-top boundary. By using different filters that penetrate varying altitudes, researchers confirmed that the wave extends vertically through multiple layers of the upper atmosphere.

Contrasting the North Pole’s Staid Hexagon

For decades, Saturn’s north pole stood alone as a meteorological wonder. Planetary scientists spent years hunting for a southern counterpart, expecting symmetrical behavior across the planet’s hemispheres.

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Yet observations spanning from Hubble’s initial 1990 runs through NASA’s Cassini spacecraft mission, which orbited Saturn from 2004 to 2017, detected no persistent geometric boundaries in the south.

The northern hexagon has remained remarkably stable for more than 40 years, whereas the southern decagon is currently strengthening and evolving.
The southern decagon shows varying darkness along its edges, pointing to an active, dynamic weather system rather than a long-stabilized structure.

Simon added, The northern hexagon has been there every time we’ve looked for more than 40 years. This feature is different — it appears to be strengthening, giving us the rare opportunity to watch a giant atmospheric pattern develop.

Unanswered Questions and Next Steps

Sánchez-Lavega noted that the discovery proves the ‘unique’ hexagon is not as extraordinary as we thought and raises intriguing parallels to the polygonal arrangement of cyclones seen at Jupiter’s poles.