Saturn's Circular Bandings Display Rainbows, and Astronomers Might Be On the Verge of Unraveling Their Cause
In a fascinating discovery, a team of researchers led by Niels Rubbrecht has identified stripe-like features resembling rainbows in the Cassini images of Enceladus's 17th close fly-by on March 27, 2012. These peculiar rainbows, observed in Saturn's E Ring, have been a subject of intrigue ever since.
The stripes, which were also apparent in two other Enceladus fly-bys in December 2010 and May 2012, are believed to be made up of particles spewing out of the moon's plumes. The researchers are not yet entirely clear why these particles are larger than those in the plumes and are inclined so far out of Saturn's rings.
The ice particles causing these rainbows create a reflection grating, diffracting the light and spreading it into its component wavelengths. The brightest band seen in the Cassini images has a wavelength of around 5μm, produced by sunlight reflecting off ice crystals. The spectrum of the bright band, as analysed by the Visual and Infrared Mapping Spectrometer (VIMS), indicates it's caused by water-ice crystals with a smattering of carbon dioxide ice, suggesting the material has been freshly ejected into space.
The relative positions of these parallel stripes were consistent between different images, angled around 16° to the plane of the Solar System. Interestingly, the separate bands making up the stripes appear to shift in position slightly when examined in different wavelengths of light.
This particular discovery of space rainbows around Enceladus is unprecedented and has a poetic beauty to it. It's a testament to the wonders that still lie hidden in our solar system, waiting to be uncovered.
The Cassini orbiter, which made these discoveries possible, discovered plumes of water-ice erupting from fissures in the moon Enceladus back in 2005. The 'light-dispersing phenomenon' observed near Enceladus is suggested to be caused by these rainbows.
Optical phenomena common in Earth's atmosphere have also been discovered in other worlds, such as a halo on Venus and hexagonal-shaped ice crystals in Martian clouds. This discovery adds to the growing body of evidence suggesting that the physics around Saturn's rings is creating a similar effect.
The article was read by Lewis Dartnell from the September 2025 issue of the website, titled "Peculiar Rainbows in Saturn's E Ring: Uncovering Luminous Bands near Enceladus" by Niels Rubbrecht, Stéphanie Cazaux et al., available online at arxiv.org/abs/2502.18028. The research team continues to study these rainbows, hoping to unravel the mysteries they hold about Enceladus and Saturn's E Ring.
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