Like Earth, Saturn's ionosphere is composed of highly charged particles. The solar wind continually slams into this region, igniting space weather phenomena such as aurorae.
In 1980, during the Voyager 1 flyby of Saturn, dark bands were detected in Saturn's upper atmosphere - it was surmised that there may be some interaction between Saturn's rings and its ionosphere. However, in follow-up studies, little further evidence for these bands was found. That was until the Keck II telescope's NIRSPEC instrument was trained on the planet in 2011.
The high-resolution near-infrared spectrograph detected the variations in the emission of a hydrogen molecule in the Saturnian ionosphere. This particular molecule - composed of three hydrogen atoms, known as trihydrogen cation (H3+) - is commonly found in space environments and has a specific emission spectrum. Normally, one would expect a uniform distribution of H3+ (as is seen in the atmospheres of Earth and Jupiter), but planet-wide bands in its distribution were discovered on Saturn.