February 4, 2022 | David F. Coppedge

Two More Age Troubles for Saturn’s Rings

Disruptive processes make it harder to believe
Saturn’s rings could last for billions of years


Gustav Holst may have called Saturn the bringer of old age, but the thing aging now may be beliefs that Saturn is old. Here are two new papers by Japanese scientists finding additional decay processes at work in Saturn’s rings.

Saturn and its rings as seen by Cassini, April 25, 2016.

Disruption of Saturn’s ring particles by thermal stress (Hirata et al., Icarus 19 Feb 2022). Knowing that thermal stress is at work on our moon to disrupt boulders and grind them down to dust, these researchers considered whether that happens in Saturn’s rings.

Spacecraft and ground-based observations show that the main rings of Saturn lack particles larger than 10 m. Tidal or collisional destruction of satellites/comets have been proposed as the origin of the main rings; however, Saturn’s tide alone cannot grind km-sized fragments into submeter-sized particles because of the high mechanical strength of water ice and rock. The question arises as to why such large particles are not left in the current ring. It is known that thermal stress induced by diurnal and seasonal temperature variations can cause weathering and fragmentation of boulders and contribute to dust and regolith production on the Moon and terrestrial planets, and then such thermal stress can break particles larger than a critical radius while cannot smaller than the critical radius. In this study, we examined the role of thermal stress acting on Saturn’s ring particles. We found that thermal stress can grind porous ring particles larger than 10–20 m, which explains the lack of particles larger than 10 m in Saturn’s ring. Also, fragmentation by thermal stress can be adoptable for the ε rings of Uranus.

The only solar system bodies with large boulders, they say further, are found in “geologically active provinces such as the tiger stripes of Enceladus, where boulders are supplied by recent geological activity.” A follow-up question should be why bodies as small as Enceladus should be active after 4.5 billion Darwin Years. That question was not asked.

Cassini dives through the gap between the D Ring and Saturn during its Grand Finale before burning up in Saturn’s atmosphere on September 15, 2017.

Dust release from cold ring particles as a mechanism of spoke formation in Saturn’s rings (Hirata et al., Icarus 3 Feb 2022). The same lead author (Naoyuki Hirata) and a co-author on the previous paper was joined by another colleague for this paper earlier in the month. The unexpected phenomenon of “spokes” running across Saturn’s rings, first discovered by Voyager 2 in 1981, still defies full explanation after Cassini’s 13-year orbital tour. The spokes appear as the ring particles emerge from shadow, observations showed, but smear out as the rings near the terminator.

The most common explanation, that of electrostatic levitation, this team says, fails because “the electrostatic force caused by such charging mechanisms is much weaker than the cohesive force acting on dust grains at ordinary conditions in the ring environment.” Another physical process must be preparing the dust particles for levitation.

Here we propose a novel model for the formation of the spokes, where the temperature dependence of cohesion plays an essential role. Ring particles with a temperature below 60 K adsorb an O2 ring atmosphere, which facilitates release of dust grains from them by a reduction in the cohesive force between the grains and the particles on the morning ansa. Then, intense electrostatic forces sufficient to overcome the cohesive force are generated on the surface of ring particles and the released dust grains form the structure of spokes. Our model explains observational features of the spokes including their longitudinal location, lifetime, radial expansion velocity, and seasonality.

Large quantities of oxygen had been detected in the tenuous ring atmosphere by Cassini in 2004 (JPL). It probably comes from collisions that release water vapor in the ring ice. As the new study proposes, some of this oxygen participates in release of dust that creates the spokes. So collisions not only create the oxygen atmosphere, but the oxygen causes further release of spoke particles—a double whammy of disruption.

Believers in deep time for the solar system have many problems, and here is a big one. They have to keep Saturn’s rings going for 4.5 billion years. Dust disruption is but one force attacking the rings constantly. Others include micrometeoroids, collisional spreading, sputtering (bombardment at the atomic scale), gas drag and light pressure (the Poynting-Robertson effect). There are additional age problems in Saturn’s moons.

Upper limits placed on the age of Saturn’s rings and moons by Cassini scientists have been 100 million years maximum, with some as low as 10 million years. Look what a tiny fraction of 4.5 billion years that is—

The burden of proof should be on old-agers to support billions of years, not on those who look at the evidence objectively and see youth.

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