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

Further study is needed from Hubble and the NASA/ESA/CSA James Webb Space Telescope, as well as analysis of computer models, to understand how the decagon formed, how long it may last, and how it compares to the long-lived hexagon in the north.

The discovery highlights one of Hubble’s greatest strengths: its long duration in operation has allowed astronomers to track changes over time in Solar System planets and other astronomical objects as well.

Rather than providing a single snapshot, the OPAL programme allows scientists to follow seasonal changes, track short-lived storms, and identify other atmospheric features that evolve slowly over time.

“When we started the OPAL programme, we expected compelling surprises but we didn’t know what to expect specifically,” said Mike Wong, study co-author, University of California, Berkeley. “A lot of the discoveries we see coming from OPAL are not just based on one observation, but on years and years of data. Regular observations over time are enabling a lot of new findings.”

The team plans to continue observing Saturn to determine whether the decagon settles into a long-lived, stable configuration like the northern hexagon or continues to evolve. Future observations also could help scientists determine what drives the wave, what it reveals about the atmospheric dynamics of giant planets throughout the Solar System, and how they may relate to those we see here on Earth.