Saturn rings sculpted by nearby moons


An article published in the journal “Science” reports new details on Saturn rings and the moons that orbit embedded in them, in particular Daphnis, in the space inside the Ring A called Keeler Division. A team of researchers used data collected by the Cassini space probe during the last months of its mission to better understand their composition and how the nearby moons sculpt them generating a greater complexity than expected. A second article written by Shigeru Ida comments on this new study.

The mission of the Cassini space probe ended on 15 September 2017 with its destruction in Saturn atmosphere but many scientists continue to analyze the data gathered during the 13 years of its extraordinary mission. In the rings’ case, a lot of information was gathered during the Ring Grazing Orbits, between December 2016 and April 2017, and the Grand Finale where it passed between the planet and its rings, between April and September 2017.

The analysis of the data revealed new details such as colors, chemistry and temperature in the rings indicated as D, C, B, the Cassini Division, A and F. It has long been known that the rings are formed mainly of water ice but the new data offer more information on the other components, including organic compounds, with some surprises.

Streaks in the F ring with the same length and the same orientation show that they were probably generated by a group of objects that hit the rings together. This indicates that the rings are shaped by flows of materials that orbit Saturn and not by objects such as cometary debris that move around the Sun that collide with the rings.

Gianrico Filacchione of the Italian National Institute of Astrophysics, Rome, among the authors of the research, explained that the denser areas of the rings appear richer in water ice and contaminants and are generally colder. He added that the measurements of the Cassini space probe’s Visible and Infrared Mapping Spectrometer (VIMS) instrument can be explained with two different types of contaminants: the ones responsible for the redness of the visible spectrum can be traced to organic materials such as tholins and polycyclic aromatic hydrocarbons or nanoparticles of iron, the other type is a neutral absorber compatible with amorphous carbon or silicate particles.

The distribution of organic materials appears to be very different in the various rings. Phil Nicholson of Cornell University, another author of this research and VIMS instrument scientist, stated that if they were in large amounts at least in the rings A, B and C they would have detected them as it happened with the flow discovered by Cassini from ring D to Saturn’s atmosphere.

The data collected show the importance of some of Saturn’s moons, which sculpt the rings in various ways. The image (NASA/JPL-Caltech/Space Science Institute) shows a false-colored mosaic with the moon Daphnis, in Keeler’s Division, generating waves in one of Saturn’s rings. The photos used for the mosaic were taken from a distance of about 28,000 kilometers (17,000 miles) from Daphnis.

Matt Tiscareno of the SETI Institute, lead author of the research, pointed out that the details on the influence of the moons provide a window into the solar system formation, where protoplanetary disks evolve under the influence of masses embedded within them.

The close-up images of the rings revealed three different textures: clumpy, smooth and streaky. Matt Tiscareno commented that they tells us that the rings appearance isn’t only a function of how much material there is but there must be something different about the characteristics of the particles, perhaps influencing what happens when two ring particles collide and bounce off each other, but they don’t yet know what it is.

The study of Saturn’s rings is far from over because there are still doubts about the processes underway that determine their evolution. Close observations that capture their structures’ details and composition are essential to provide answers but to start new space missions to Saturn it will take at least several more years. Meanwhile we can enjoy the images provided by the Cassini space probe of this great cosmic show.

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