NASA's Hubble Space Telescope has photographed a giant, ten-sided wave circling Saturn's south pole, the first large and regularly shaped jet-stream pattern astronomers have documented in the planet's southern hemisphere. The finding, detailed in a NASA announcement published this month, gives Saturn a southern counterpart to its long-studied northern hexagon.
The decagon first appeared faintly in Hubble data around 2023 and grew sharp enough for ground-based telescopes to confirm by 2024 and 2025, researchers said. Unlike the hexagon, which has held a stable six-sided shape since the Cassini spacecraft and its predecessors first mapped it decades ago, the new pattern extends through multiple layers of Saturn's atmosphere and, according to the team, is actively strengthening rather than settling into a fixed form.
The discovery came out of the Outer Planet Atmospheres Legacy program, which has photographed the solar system's outer planets annually for more than a decade, with amateur astronomers Trevor Barry and Jean-Paul Oger providing early ground-based observations that pointed researchers toward the feature, according to a summary of the peer-reviewed study.
A four-decade search
Planetary scientists had been looking for a southern match to the hexagon for decades. "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 Agustín Sánchez-Lavega of the University of the Basque Country in Spain, who led the study.
We've never seen anything quite like this in Saturn's southern hemisphere.
Amy Simon, NASA Goddard Space Flight Center
Simon, who leads the OPAL program, said the bigger puzzle is timing. "The question is, why did it suddenly form now when we haven't seen one before?" Co-author Mike Wong of the University of California, Berkeley, credited the discovery to the program's steady cadence of observation: "Regular observations over time are enabling a lot of new findings."
The research team plans to keep watching the decagon with Hubble and, eventually, the James Webb Space Telescope, to see whether it stabilizes into a hexagon-like fixture or dissipates entirely. The results were published Sept. 3 in the journal Science Advances.
