Unexpected Geometry at Saturn’s South Pole
Astronomers have identified a 10-sided geometric formation circling Saturn’s south pole. This feature, termed a decagon by researchers, appeared in recent images captured by the Hubble Space Telescope. While Saturn is known for a stable 8-sided hexagon at its north pole, a similar pattern in the southern hemisphere represents a first for planetary science. The feature sits within a high-speed jet stream, with winds in the area reaching 800 kilometers per hour.
Observation of the decagon began through a combination of professional and amateur data. Agustín Sánchez-Lavega, an astrophysicist at the University of the Basque Country, initially noticed irregularities in images provided by the Planetary Virtual Observatory Laboratory. Amateur astronomers Trevor Barry and Jean-Paul Oger first flagged a faint band in 2024, which led the team to look closer at past records. Hubble data eventually confirmed the existence of this atmospheric structure dating back to 2023.
The Search for a Southern Counterpart
For decades, scientists looked for a southern equivalent to the long-standing northern hexagon. The Cassini spacecraft, which orbited the planet from 2004 to 2017, provided detailed maps of the atmosphere but revealed no such long-lived geometric formation. That said, the planet’s shifting seasons have now tilted the south pole into a better viewing angle for Earth-based telescopes. This change allowed the team to track the development of the decagon as it emerged.
"Given Saturn’s symmetry in its north-south jet stream system, we have been searching for a counterpart to Saturn’s northern hexagon on the south pole in Hubble images since 1990," said Sánchez-Lavega. The discovery highlights how much of the giant planet’s atmospheric behavior remains hidden from view for long stretches of time. It reinforces the value of multi-year observational data in identifying slow-moving planetary shifts.
Understanding the Atmospheric Engine
This decagon extends deep into the atmosphere rather than existing as a shallow cloud-top feature. By using multiple wavelengths of light, Hubble captured images that suggest the wave influences several vertical layers of the planet’s gaseous exterior. Researchers are now working to determine the physical drivers behind this wave formation. They expect to use computer modeling to simulate the pressure and thermal conditions that allow such a rigid shape to manifest in a fluid gas environment.
"The most intriguing part to me is that this seems to have just formed recently," says Amy Simon of NASA’s Goddard Space Flight Center. Unlike the northern hexagon, which has persisted for at least 40 years, the decagon appears to be in an active state of growth. Scientists will now turn to the James Webb Space Telescope to provide a clearer picture of the temperatures and chemical composition within the storm. The long-term stability of this structure is still unknown, leaving observers to watch for further changes in the coming years.