A Bizarre Southern Decagon
Perhaps the most stunning recent discovery is a massive, 10-sided atmospheric wave, or 'decagon', encircling the south pole. This is a huge deal because for decades, scientists have been fascinated by a stable six-sided hexagon at the north pole, with
no southern counterpart. Thanks to Saturn's long, 29-year orbit, its south pole was hidden from Earth's view for over a decade, but as it tilted back, Hubble was waiting. In observations from 2023, and with increasing clarity through 2025, Hubble provided the first clear evidence of this new, evolving geometric pattern, something even the Cassini spacecraft, which orbited Saturn for 13 years, never saw. This gives scientists a rare chance to watch a giant planetary weather pattern form in real-time.
The Dynamic Southern Aurora
Just like Earth, Saturn has auroras — beautiful curtains of light that dance around its poles. But Saturn's are a bit different, and Hubble is uniquely equipped to study them. By capturing images in ultraviolet light, which is invisible to the human eye, Hubble has provided the most detailed views of Saturn's southern aurora. These observations show a glowing ring of light that can change daily, sometimes moving around and sometimes staying still. Unlike Earth's relatively brief auroral storms, Saturn's can last for several days. Hubble’s data helped show that these powerful displays are driven largely by the solar wind, the stream of charged particles flowing from the Sun.
Tracking Long-Term Seasonal Change
Hubble's greatest strength is its longevity. Orbiting above Earth's blurry atmosphere, it can take consistent, high-quality images of planets over many years. This is crucial for a planet like Saturn, where each season lasts for more than seven Earth years. The Outer Planets Atmospheres Legacy (OPAL) program uses Hubble to annually check in on the gas giants. This long-term monitoring has allowed astronomers to directly observe seasonal changes at the south pole, including shifts in the colours of atmospheric bands and changes in the polar haze as the pole has moved from its summer into autumn.
Confirming a 'Warm' Polar Vortex
It sounds strange for a planet so far from the Sun, but Saturn's south pole has a hot spot. Well, 'warm' is more accurate. Before the Cassini spacecraft plunged into Saturn's atmosphere, it detected a surprising vortex of warm air right at the south pole. Hubble's long-range observations played a key role in supporting and providing context for these findings. By tracking temperatures from afar, Hubble helped confirm the existence of this unusual feature, where temperatures were significantly warmer than the surrounding atmosphere. This discovery challenged scientists' understanding of how heat is distributed and circulated in the atmosphere of a gas giant, revealing that the dynamics at the poles are far more complex than previously thought.
Monitoring Wind Speeds and Jet Streams
Saturn is a world of extreme weather, with winds that can blow at over 1,600 kilometers per hour. Hubble's sharp vision allows astronomers to track individual cloud features over time, helping them map the powerful jet streams that circle the planet, including those that cage the poles. By comparing images taken years apart, scientists can measure how wind speeds change. For instance, data from Hubble showed that winds near the equator had actually changed speed between the time of the Cassini mission and later observations. This ability to monitor the planet's fundamental atmospheric engine, even from over a billion kilometers away, is essential for understanding what drives strange features like the newly discovered decagon.
