Saturn’s Rings Officially Young (Again)
Old agers can’t weasel around it any more.
Saturn’s rings are short-lived and young.
— If Saturn is as old as claimed, its rings appeared in the last 1/45th of its existence. —
Every time Saturn’s rings are discussed in the journals and astronomy news sources, we check to see if some new theory can make them last for billions of years. Two new papers in Icarus, the leading journal for planetary scientists, offer no hope for believers in deep time. Instead, they give multiple reasons why the rings cannot be old.
We’ve shown this diagram multiple times, because it illustrates the quandary. The solar system is said to be 4.5 billion years old. The rings, though, cannot be older than about a few 100 million years, both papers agree. That sounds like a lot of time, but 100 million years is a tiny fraction of the assumed age, as shown by the red bar. It would represent less than one foot on a 45-foot rope. 10 million years (shown as the purple line) is one-tenth of that! A million years is one tenth less, and so on, such that shorter ages vanish into insignificance on such a scale.
If the rings were the only problem, that would be bad enough. But two other independent measurements exacerbate the problem: Titan’s atmosphere, and the geysers of Enceladus: both must be less than 100 million years old, experts say. These estimates, remember, are “upper limits” on age. They could be far younger. The upper limit to the rings’ age is not an actual age, but a maximum. Assigning an upper limit can be a gross exaggeration, like saying, “A skyscraper cannot be taller than the distance to the moon.”
What This Does to Deep Time
A logical follow-up question to the finding that 100 million years is an upper limit is to ask how they know whether 4.5 billion years for Saturn is true. With our 45-foot rope analogy, if one foot on the near end of the rope is a maximum lifetime for the rings (and for Enceladus and Titan’s atmosphere), how do they know the other 44 feet existed? Look at the diagram again. It takes a lot of faith to believe that anything left of the red line is real.*
*Note: Upper limits are easier to establish than lower limits. The reason is that the observation-to-assumption ratio is higher, which is a desirable thing in science. It’s more empirically modest to claim an upper limit (i.e., ‘this phenomenon cannot be older than x years”) than a lower limit (‘i.e., ‘this phenomenon must be at least y years old’). For the upper limit, one can take observed measurements of rates and extrapolate them a reasonable distance back in time without making unwarranted assumptions. This maintains a high observation to assumption ratio. For the lower limit, one would have to extrapolate observed rates recklessly into the unobserved past. This lowers the observation to assumption ratio, giving more weight to assumptions instead of to empirical measurements.
Secular planetary scientists do not like to entertain thoughts that humans appeared on Earth in a “special time” to be able to enjoy Saturn’s glorious rings. It makes them uncomfortable. They preferred believing that the rings appeared with Saturn billions of years ago, until the evidence could no longer be doubted. Are we also living in a special time to enjoy total solar eclipses, Pluto’s ice volcanoes, rubble pile asteroids that should have busted apart long ago, comets, asteroids with orbiting moons, resurfacing activity on Mercury, the volcanoes of Venus, activity on the moon, the Earth’s ideal magnetic field, and dozens of other lucky “coincidences” that scientists have found? The case of Saturn’s rings is colorful and interesting, but it is only one in a class of examples showing that the solar system appears young. Find many more of these in our Solar System and Dating Methods categories. Incidentally, if Saturn’s rings are young, the ephemeral rings at Jupiter, Uranus and Neptune must be even younger, because they are subject to the same disruptive forces.
The New Papers
As we will see, the authors of the new papers still believe in the 4.5 billion year age for Saturn and the solar system. But they cannot explain why the rings appeared recently without special pleading.
Constraints on the initial mass, age and lifetime of Saturn’s rings from viscous evolutions that include pollution and transport due to micrometeoroid bombardment (Estrada and and Durisen, Icarus, Aug 2023 issue).
The Cassini spacecraft provided key measurements during its more than twelve year mission that constrain the absolute age of Saturn’s rings. These include the extrinsic micrometeoroid flux at Saturn, the volume fraction of non-icy pollutants in the rings, and a measurement of the ring mass. These observations taken together limit the ring exposure age to be a few 100 Myr if the flux was persistent over that time (Kempf et al., 2022). In addition, Cassini observations during the Grand Finale further indicate the rings are losing mass (Hsu et al., 2018; Waite et al., 2018) suggesting the rings are ephemeral as well.
One notable finding is that rings darken quickly from micrometeoroid impacts. This means that one cannot assume that the initial rings started out much larger and are therefore older.
We find that regardless of initial mass, the ring always ends up with more pollutant than is currently observed, because the ring spends the majority of its lifetime at relatively low mass where it is most susceptible to darkening.
The authors spend a few paragraphs discussing various “scenarios” for the origin of the rings in deep time, but give five reasons why the rings had to form recently, based on Cassini data. Those scenarios for ancient rings begin sounding like special pleading: i.e., storytelling to keep the rings old in spite of the observations.
Large mass inflow rates in Saturn’s rings due to ballistic transport and mass loading (Durisen and Estrada, Icarus, Aug 2023 issue). In this companion paper, the same two authors consider other forces and measurements that constrain the age of the rings.
The Cassini mission provided key measurements needed to determine the absolute age of Saturn’s rings, including the extrinsic micrometeoroid flux at Saturn, the volume fraction of non-icy pollutants in the rings, and the total ring mass. These three factors constrain the ring age to be no more than a few 100 Myr (Kempf et al., 2022). Observations during the Cassini Grand Finale also showed that the rings are losing mass to the planet at a prodigious rate. Some of the mass flux falls as “ring rain” at high latitudes. However, the influx in ring rain is considerably less than the total measured mass influx of 4800 to 45000 kg s−1 at lower latitudes (Waite et al., 2018).
Some of the mass inflow is caused by continuous micrometeoroid impacts on the rings, which splash material out of the ring plane and toward Saturn. Based on “ring rain” measurements, Durisen and Estrada set upper limits of 15 to 400 million years for the rings, a very wide margin (but still a tiny fraction of the assumed age of Saturn). But that’s only one factor. Micrometeoroids pollute the rings with dark dust, and yet the rings appear surprisingly clean. From those measurements, the authors estimate on the young side.
From these mass inflow rates, we estimate that the remaining ring lifetime is 15 to 400 Myr. Combining this with a revised pollution age of 120 Myr, we conclude that Saturn’s rings are not only young but ephemeral and probably started their evolution on a similar timescale to their pollution age with an initial mass of one to a few Mimas masses.
Here is their inescapable conclusion: “The age and future lifetime of the rings are likely to be much shorter than the age of the Solar System.”
Update 13 May 2023: No sooner had we gone to press with the story than another independent source joined in. The press release and paper are from Sascha Kempf at UC Boulder, one of the principal investigators of the Cassini mission. He managed the bucket-shaped Cosmic Dust Analyzer (CDA) on the spacecraft (see photo, right).
How old are Saturn’s rings? Far younger than once thought, according to new study (University of Colorado at Boulder, 12 May 2023). By “far younger” they mean hundreds of millions of years, as the other papers estimate, but again, this is far, far too young to explain in traditional evolutionary Deep Time. Notice also that no matter how the evidence points, they still maintain their consensus Age of the Solar System.
A new study led by physicist Sascha Kempf at CU Boulder has delivered the strongest evidence yet that Saturn’s rings are remarkably young—potentially answering a question that has boggled scientists for well over a century.
The research, published May 12 in the journal Science Advances, pegs the age of Saturn’s rings at no more than 400 million years old. That makes the rings much younger than Saturn itself, which is about 4.5 billion years old.
Kempf is aware that a great physicist theorized about the nature of the rings: see our biography of Maxwell, a Bible-believing Christian with a reputation close to that of Newton and Einstein.
“In a way, we’ve gotten closure on a question that started with James Clerk Maxwell,” said Kempf, associate professor in the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder.
The new data, collected by Cassini between 2004 and 2017, shows that cosmic dust continually flows through the solar system, collecting on ring particles like dust bunnies. The dust should make them dirty in time, but the rings are remarkably clean. They still are 98% water ice by volume. Even if one gram of dust collected per year on every square foot of the rings, it would add up to a substantial amount over time. And that’s not all; added to that measurement, there is also the “ring rain” of material falling into Saturn mentioned in the press release.
The paper by Kempf et al. is open-access at the AAAS journal Science Advances. The paper estimates “a ring exposure time ≲100 to 400 million years in support of recent ring formation scenarios.” See quote from the paper below* giving reasons why the age was probably far less.
The youth of Saturn’s rings is not news; it was a vexing problem when I was at JPL working on the Cassini mission. I discussed it with some of the leading “ringmasters” at the lab, whose names and reputations are renowned on this subject, and some who are listed as authors on these and earlier papers. CEH has been following the story for two decades and has posted articles about almost every new announcement from the planetary science community.
What these three new papers offer is confirmation that no new theory is forthcoming to keep the rings old, and that options have basically run out. The rings are young. And if they are far younger than Saturn, then why believe Saturn is old? Why trust lucky “scenarios” for having rings appear recently just a few hundred million years ago (or less)? It sounds like special pleading, and it is (see Robin Canup‘s “lucky Titan-sized moon” story for example). They want old rings, but can’t have them. Look how Kempf is left dumbfounded:
That these ephemeral features existed at a time when Galileo and the Cassini spacecraft could observe them seems almost too good to be true, Kempf said—and it begs an explanation for how the rings appeared in the first place. Some scientists, for example, have posited that Saturn’s rings may have formed when the planet’s gravity tore apart one of its moons.
“If the rings are short lived and dynamical, why are we seeing them now?” he said. “It’s too much luck.”
If it begs for an explanation, we have one: Saturn and the solar system really are young. Why is that out of the realm of possibility, when the evidence points that way? Isn’t that a better scientific method than luck, the Stuff Happens Law, in this case applied to planetary science?
Removing the possibility of ancient rings is a bit like playing Jenga, where the tower of sticks represents the assumed age of the solar system. You can keep the tower standing for awhile as individual sticks are carefully removed, but sooner or later, the pile comes crashing down. In my experience, the pile has already collapsed and only exists in the imaginations of Deep Time diehards. Get ahead of the game. Kick the Deep Time habit. It only exists to give Darwinians the millions and billions of years they rely on. But Humpty Darwin has fallen already for many other reasons, so making additional reckless drafts on the bank of time doesn’t help him any more.
*Quote from the Kempf paper:
We find that the ring exposure age for the current mass influx into the Saturnian system does not allow the rings to be formed together with Saturn and its satellites nor slightly later during the Late Heavy Bombardment. Saturn’s current rings cannot be primordial. An initially massive primordial ring has been posited to better resist the effects of pollution as it viscously evolves to its current state over billions of years. However, viscous evolution of such a massive ring occurs quickly, so that the ring spends the vast majority of its lifetime near its current mass and would absorb a much higher-than-observed volume fraction of pollutants during that time. Moreover, the IDP flux [interplanetary dust particles inflow rate] at Saturn F∞ might well not have been constant throughout the solar system’s history: It was probably larger in the early days, further complicating such an old-ring scenario.