A view captured by Cassini of Saturn casting a shadow across its main rings

Data from the final days of the Cassini mission to Saturn have detailed how the planet’s moons shape its rings. Credit: NASA/JPL-Caltech/Space Science Institute

Planetary science

A last close-up of Saturn’s rings reveals the mark of its moons

Despite their small size, some of the planet’s moons create clumps and ripples in its brilliant halo.

The final transmissions of NASA’s Cassini spacecraft have shown, in superb detail, how Saturn’s petite moons sculpt the giant planet’s rings.

After 13 years studying Saturn, Cassini plunged to its end in the planet’s atmosphere in 2017. But before its demise, the craft flew between Saturn and its rings, snapping images all the while.

Matthew Tiscareno at the SETI Institute in Mountain View, California, and his colleagues analysed the resulting close-ups, which provide a trove of details. For example, the images show that as ring particles pass by and trail behind the moon Daphnis, which is just 8 kilometres across, they form a series of ripples that deteriorate over time.

Cassini’s images also reveal that some rings contain narrow bands with a clumpy, straw-like texture. Such bands might form when ring particles with particular properties collide and bounce off one another. And images taken at different wavelengths show variations in the rings’ colour, which might be explained by disparities in the rings’ thickness.