Saturn south pole decagon: NASA Hubble detects mysterious 10-sided pattern forming around planet

Saturn’s south pole has revealed an atmospheric feature unlike anything previously observed there. Recent observations from NASA’s Hubble Space Telescope have identified a huge, evolving 10-sided wave wrapped around the planet’s southern pole, according to information provided by NASA on its website.

The structure resembles Saturn’s well-known six-sided jet stream pattern at the north pole, but scientists say the newly observed feature is behaving differently. Rather than appearing as a long-established formation, the southern structure seems to be strengthening, giving researchers an opportunity to observe an atmospheric pattern while it develops.

The findings were published Wednesday in Science Advances.


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Hubble catches Saturn’s new southern pattern

According to NASA, researchers pieced together several years of Hubble observations dating back to 2023 to establish that the feature was already beginning to emerge.

The observations were collected through Hubble’s Outer Planet Atmospheres Legacy, or OPAL, programme, which has monitored the outer planets each year for more than a decade.

Amy Simon, a study co-author and OPAL principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said the southern phenomenon does not resemble anything previously detected there.

“We've never seen anything quite like this in Saturn's southern hemisphere,” Simon said, according to NASA.

She noted that the northern hexagon has remained visible whenever scientists have observed it for more than 40 years. The southern feature, by contrast, appears to be growing stronger.

Astronomers first spotted clues from Earth

The discovery did not begin with Hubble. Saturn’s changing seasons gradually brought its southern pole into a better viewing position from Earth, allowing astronomers to examine the region more closely.

Agustín Sánchez-Lavega, lead author of the study and a researcher at the University of the Basque Country in Spain, and amateur astronomers Trevor Barry and Jean-Paul Oger first noticed an unusual wavering band in ground-based images in 2024.

Those observations were submitted to the Planetary Virtual Observatory Laboratory, a University of the Basque Country website that collects images of Solar System planets from observers worldwide.

Additional ground-based images captured in 2025 showed stronger indications that the feature could be developing into a decagon, or 10-sided structure.

Scientists then turned to Hubble for sharper observations from space.

How the 10-sided structure differs from Saturn’s hexagon

Hubble’s advantage is its ability to observe Saturn without Earth’s atmosphere interfering with the images. It can also capture the planet across full rotations with high spatial resolution, allowing researchers to study the feature in greater detail.

Sánchez-Lavega said scientists had been searching for a southern counterpart to Saturn’s northern hexagon in Hubble observations since 1990 because the planet’s northern and southern jet-stream systems are broadly symmetrical.

NASA said earlier observations from the Cassini spacecraft, which orbited Saturn from 2004 to 2017, showed no sign of a long-lived formation of this type in the southern hemisphere.

Hubble data, however, confirmed that the structure was present as far back as 2023.

The feature stretches through Saturn’s atmosphere

According to NASA, the wave sits within one of Saturn’s strong jet streams and extends across several atmospheric layers.

That suggests the phenomenon is more than something occurring only at the visible cloud level. Its position also appears to shift slightly depending on the wavelength used to observe it because different wavelengths allow scientists to examine different altitudes in Saturn’s atmosphere.

For researchers, that vertical extent makes the feature particularly significant.

Simon described its recent emergence as one of the most intriguing aspects of the discovery, raising the question of why such a pattern appears to have formed now after not being detected previously.

“The most intriguing part to me is that this seems to have just formed recently,” Simon said, according to NASA. “The question is, why did it suddenly form now when we haven't seen one before?”

What scientists still do not know

Researchers do not yet know how the decagon formed, how long it will survive or whether it will eventually settle into a stable configuration.

Further observations from Hubble and NASA’s James Webb Space Telescope, together with computer modelling, could help answer those questions. Scientists also want to determine how the southern pattern compares with the persistent hexagon around Saturn’s north pole.

The answers could provide broader insight into how atmospheric systems operate on giant planets.

Why long-term Hubble observations matter

The discovery also highlights the value of observing planets repeatedly over long periods rather than relying on individual images.

NASA’s OPAL programme has allowed astronomers to monitor seasonal changes, follow temporary storms and identify atmospheric structures that evolve gradually.

Mike Wong, a study co-author at the University of California, Berkeley, said many OPAL discoveries have emerged only after researchers compared years of observations.

“When we started the OPAL program, we expected compelling surprises, but we didn't know what to expect specifically,” Wong said, according to NASA.

He added that sustained observations were enabling scientists to uncover new phenomena that could not have been identified from a single snapshot.

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Scientists will keep watching Saturn’s south pole

The research team plans to continue monitoring the feature to determine whether it becomes a stable, long-lasting structure like the northern hexagon or continues changing.

Future observations could also help establish what drives the wave and what it reveals about atmospheric processes on giant planets. Scientists hope such findings could eventually improve understanding of planetary atmospheric dynamics across the Solar System, including how some of these processes compare with phenomena observed on Earth.

NASA said Hubble’s more than three decades of operation have enabled astronomers to track changing features across planets and other astronomical objects, making long-term observations an important part of its scientific legacy.