"Rainbow" in Saturn's rings: Unusual glowing stripes were observed near Enceladus.

In 1966, a previously unknown ring was discovered around Saturn, which turned out to be unusual: instead of being flat like the others, it takes the form of a torus, a "bagel," and interestingly, it follows the orbit of Saturn's small, pristine moon, Enceladus.

During 1980-1981, the Voyager 1 and Voyager 2 probes flew past the moon in succession and sent back its first images. It became clear that a roughly 500-kilometer icy sphere orbits the gas giant, which is why the moon appears so bright. The presence of water ice on its surface is evident from the spectrum of the reflected light.

Even back then, suspicions arose that Enceladus might not be completely frozen, suggesting the possibility of a global ocean beneath the ice. Scientists proposed a potential heat source to keep the water in a liquid state inside such a small, cold celestial body far from the Sun — the so-called tidal heating: as the moon moves around Saturn, the planet's gravity subtly deforms and "kneads" Enceladus, creating friction within it.

All these discoveries and hypotheses came together when the Cassini probe captured images of gigantic geysers erupting from the southern polar region of Enceladus in 2005. Firstly, suspicions about the subsurface ocean were strengthened. Secondly, it became clear that this water vapor erupting from beneath the surface creates a distinctive toroidal ring E around Saturn.

Recently, astronomers from the Netherlands, France, and the USA added an intriguing detail. They thoroughly reviewed the data that Cassini transmitted during its flybys of Enceladus. It turned out that during three encounters with the moon, the probe recorded unusual optical effects. These effects were particularly pronounced during the flyby at the end of March 2012.

At that time, several hundred thousand kilometers from Enceladus, the spacecraft captured parallel bright bands. They were oriented at an angle of 16 degrees relative to the plane of the ecliptic, which is the plane of the planets' rotation around the Sun, and 43 degrees to the plane of Saturn's rings. As the probe and Enceladus moved closer, the bands disappeared, but soon a larger bright area emerged in their place. Researchers reported this in a recent article available on the preprint server arXiv.

Astronomers believe that these phenomena are caused by the diffraction of light: when it passes through the E ring formed by Enceladus's eruptions, it encounters countless obstacles in the form of ice particles. This creates a natural diffraction grating. Light waves bend around the obstacles, pass between the particles, meet, and overlap, leading to interference.

Scientists noted interesting details: judging by the spectrum of these bright bands, they are created by light passing among larger particles than those observed in the E ring. There are considerations that these larger particles are less prone to fragmentation due to cosmic radiation and collisions or might even combine with one another.

Additionally, the "rainbow" indicates the presence of frozen carbon dioxide particles among the ice, which are also not detected in the E ring and generally do not persist in space for long. All this suggests that the phenomenon was caused by material recently expelled by Enceladus, likely forming a separate, highly inclined structure within the E ring.