Astronomers detect a 10-sided decagon forming at Saturn's south pole

Overview

Updated Sep 6

Saturn's north pole has worn a six-sided hexagon for more than 40 years. Now Hubble Space Telescope images show a 10-sided decagon emerging at the planet's south pole — the first large polygonal jet pattern ever seen in that hemisphere.

The wave spans roughly 168,000 kilometers and sits near 60 degrees south latitude, riding an eastward jet stream that moves about 420 kilometers per hour. It rotates slowly, taking about 800 days for one full turn.

Amateur astronomers analyzing ground-based images first flagged the odd shape, and archival Hubble observations show the structure emerging as early as 2023. The decagon sharpened into a clear pattern by 2025. Scientists will track whether it stabilizes like the northern hexagon, breaks apart, or strengthens as Saturn's southern summer peaks in 2032.

Why it matters

The decagon is a live experiment in planetary atmosphere physics — watching a giant geometric wave either stabilize like Saturn's hexagon or break apart.

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Key Indicators

Number of sides in the wave

The decagon is the first large polygonal jet pattern seen in Saturn's southern hemisphere.

~168,000 km

Width of the decagon

Each side measures about 16,800 kilometers.

~800 days

Time for one full rotation

The wave crawls compared to the 420 km/h jet stream carrying it.

2023

Year the structure began forming

Archival Hubble images show subtle hints of the decagon starting in 2023.

Voices

Curated perspectives — historical figures and your fellow readers.

People Involved

Agustin Sanchez-Lavega

Lead author of the decagon study, planetary scientist

Leading the team tracking the wave's evolution

Amy Simon

OPAL principal investigator, NASA Goddard Space Flight Center

Co-author of the decagon study

Michael Wong

Planetary scientist, UC Berkeley Space Sciences Laboratory

Co-author of the decagon study

Organizations Involved

Hubble Space Telescope

Space telescope

Primary instrument tracking the decagon

Space telescope operated by NASA and ESA that has photographed the outer planets annually since 2014 through the OPAL program.

NASA Goddard Space Flight Center

Federal research center

Leads the OPAL program, co-authored the decagon study

NASA center that leads Hubble's Outer Planet Atmospheres Legacy program and co-authored the decagon study.

University of the Basque Country

Public university

Lead institution for the decagon study

Public university in Bilbao, Spain, whose planetary scientists led the decagon study.

UC Berkeley Space Sciences Laboratory

University research lab

Co-authored the decagon study, analyzed the anticyclone

Research lab that co-authored the decagon study and analyzed the anticyclone vortex possibly driving the wave.

Timeline

November 1980 September 2026

5 events Latest: September 3rd, 2026 · 2 months ago

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September 2026
Team announces decagon discovery in Science Advances
Latest Publication

Researchers from Spain, NASA, and UC Berkeley publish the decagon's characterization, dynamics, and formation hypothesis.
September 3rd, 2026
2025
Anticyclone at 55 degrees south darkens, decagon sharpens
Observation

A compact anticyclone vortex darkens sharply, and the decagon pattern becomes clearly defined in Hubble images.
2025
January 2023
Archival Hubble images show first subtle hints of decagon
Observation

Hubble's OPAL program images begin to show faint traces of a 10-sided pattern near 60 degrees south latitude.
January 1st, 2023
July 2004
Cassini observes partial southern hemisphere structure
Observation

The Cassini spacecraft observed a partial polygonal structure in Saturn's southern hemisphere, but its dynamics were never characterized.
July 2004
November 1980
Voyager 1 flies past Saturn, reveals north polar hexagon
Discovery

Voyager 1's flyby captured the six-sided jet pattern at Saturn's north pole, later confirmed by Voyager 2 in 1981 and identified in the data by 1988.
November 12th, 1980

Scenarios

Decagon stabilizes into long-lived wave like Saturn's hexagon

Possible Resolves by End of 2032

Discussed by: Agustin Sanchez-Lavega and the study team, citing the north polar hexagon's 40-plus years of persistence

The decagon may settle into a stable equilibrium with its surrounding jet stream, mirroring what the hexagon did after the vortex near it disappeared in the 1980s. Amy Simon told ESA the feature 'appears to be strengthening.' If it stabilizes, scientists would have two polygonal waves on one planet, suggesting these patterns are common on gas giants.

Decagon breaks apart as a transient atmospheric feature

Possible Resolves by End of 2029

Discussed by: Sanchez-Lavega, noting southern hemisphere zonal winds are weaker than those sustaining the hexagon

Some sides of the decagon appear fuzzy and vary in brightness, which the team reads as instability. Sanchez-Lavega's shallow-water models show polygonal waves can form and then dissipate. Saturn's southern jet streams are weaker than the northern stream that holds the hexagon, so the decagon may lack the energy to survive. The wave would fade over the next few years.

Decagon strengthens as southern summer solar radiation peaks

Uncertain Resolves by End of 2032

Discussed by: Sanchez-Lavega, writing in Scientific American about seasonal insolation peaking around 2032

Saturn's southern hemisphere is moving through spring toward summer, tilting increasingly toward the Sun. Solar insolation at the decagon's latitude peaks around 2032. If seasonal heating drives the wave, the pattern should become more pronounced each year. 'It may well become more pronounced in the coming years, when insolation reaches its peak at the latitude of the decagon around the year 2032,' Sanchez-Lavega said.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

1980-1988

Saturn's north polar hexagon (1980-1988)

Voyager 1 and 2 flew past Saturn in 1980 and 1981 and photographed a striking six-sided cloud pattern circling the north pole. Researchers identified the hexagon in the Voyager data by 1988. The Cassini mission later confirmed it with decades of close observations.

Then

Scientists spent years trying to explain how a jet stream could carve a near-perfect hexagon.

Now

The hexagon became the benchmark for polygonal planetary weather and has persisted through every observation since.

Why this matters now

The newly discovered decagon is the first large polygonal wave found in Saturn's southern hemisphere. Its evolution will show whether such patterns are common on gas giants or a one-off.

1831-present

Jupiter's Great Red Spot (1831-present)

Astronomers have continuously observed Jupiter's Great Red Spot, an anticyclone wider than Earth, since the 1830s. It has shrunk in recent decades but remains a distinct feature after nearly two centuries.

Then

The spot became the benchmark for long-lived planetary storms.

Now

It fed the assumption that giant-planet weather features persist for very long stretches, which the decagon now challenges.

Why this matters now

The study team notes features like the Great Red Spot create the impression that outer planets are timeless. Saturn's decagon, appearing and changing within a few years, shows how changeable these planets can be.

1989-1994

Neptune's Great Dark Spot (1989-1994)

Voyager 2 photographed a large dark storm in Neptune's atmosphere in 1989. When the Hubble Space Telescope looked again in 1994, the spot had vanished.

Then

The spot was the first major planetary storm observed to disappear between campaigns.

Now

It proved giant-planet weather features can be transient, appearing and vanishing within a few years.

Why this matters now

The decagon may be similarly transient. Its fate will show which planetary weather patterns endure and which evaporate.