The “Youthful” Dynamics of Saturn’s Rings – A Preemptive Anti-Young-Earth Creationism Post

Introduction

Several months ago, I posted on a young-Earth Creationism (YEC) article about uranium-238 radiometric dating of the solar system. In that article, I stated that I had one of my numerous psychic premonitions when I read the original science article that the creationists would use it somehow. But, I had no documentation backing that premonition up so I can’t apply for the James Randi Educational Foundation’s $1 Million prize. Darn.

In a much earlier post, nearly a year ago, I wrote a post on more YEC claims that the Saturnian system is young. I mentioned that they were indirectly using my own research in their claims.

Now, a year later, the science journal Icarus has its April special “Cassini at Saturn” edition out, and I happen to have a first-author paper in it. In addition, on Friday, the March 19, 2010 issue of the very prestigious journal Science has a 5-page article that kinda summarizes several of the papers in Icarus – including citing mine – that show that Saturn’s rings aren’t just boring slabs of particles orbiting away.

Call me “psychic,” but I have a feeling that some YECs will be using this in another of their attempts to propagate their version of a literal biblical worldview. This post is an attempt to summarize my own research on the rings and to show why the dynamics that we see are fully consistent with an old ring system.

Warning: This blog post rambles a bit more than usual. In it, I outline how models are created in astronomy, how that applies to the mass of Saturn’s rings, how the mass is linked to the age of the rings, and then my own research into the mass and hence age. It’s really a background post so that if/when the YECs pick up on this story I can just refer to it for background and just address the claims on that post.

How a Scientist Starts a Model

The entire purpose of physics is to mathematically produce a model that replicates the observable world. When a scientist starts out to create a model of a complicated system – say, Saturn’s rings – they will start with the simplest model possible and then add layers onto it in complexity.

Very early on, the rings were thought to be solid – thin disks that orbited Saturn. Later, that view changed to one where individual particles were thought to make up the rings. That’s the view we hold today.

In terms of the dynamics involved, in modeling the rings, one starts with a bunch of particles in orbit around a large central mass (the planet), and uses basic physics to describe how they would interact with each other. By adjusting parameters such as how big the particles are, how many there are, etc., you will get different results, and you can use the observable data to then constrain your model.

Some basic parameters that are still somewhat unknown about Saturn’s rings are the makeup of individual particles, their density, how “sticky” they are, how large they are, and how much material is actually there.

Old Voyager Results

Around the time I was born, the starship Voyager spacecraft (1 and 2) passed by Saturn. One of the many observations they made is called a “stellar occultation” through the rings. An “occultation” is when you block out a background object with a foreground one. In this case, a “stellar occultation” is when a star is blocked out, and this was by Saturn’s rings. The purpose was to measure how much light got through the rings in order to measure their “optical depth.” “Optical depth” is, well, how much light can get through something. An optical depth of 0 means that everything gets through.

Anyway, based on the Voyager measurements, which showed significant optical structure in the light that got through the rings, we had to complicate our models. And by “we” and “our” I mean the ring-studying community … I hadn’t quite entered kindergarden. The rings were still modeled as particles, but they were modeled like “granola bars” (in what is referred to as a “granola bar model”): Slabs of optically thick (no light gets through) clumps/aggregates of ring particles separated by optically thin (light gets through) gaps. In developing their models, the question now focussed on the width of those slabs and the width of the gaps between them.

It was from these models that values are still quoted today in terms of the height of the rings (“several yards” – though some places say “less than a mile”), the mass of the ring system (around the mass of the moon Mimas), and perhaps most importantly for this discussion, the age of the ring system.

The Copernican Principle

There’s a principle in astronomy that states, “We do not live in a unique time nor place until shown otherwise.” I’m not going to argue here whether that’s a good principle to live by and do research by, what its roots are, nor its “validity.” Regardless, it’s there and I personally think it’s fairly good to stick with for the time being because it forces us to do more work.

What came out of the Voyager results is that the ring system seemed “young.” “Young” here is in quotes because it means something on the order of 100 million years. That’s only 2.5% the age of the solar system, hence “young.” Part of the reason for this is that the “dynamical lifetime” of the rings of that mass is much less than the age of the solar system — the ring particles are slowly raining down on Saturn and in the future the ring system will be gone. But, that unsettles astronomers because of this principle that we don’t live in a unique time nor place.

It also makes different formation mechanisms much more difficult to justify statistically. In other words, it is much easier to justify, for example, two moons crashing together – or a moon and a large asteroid or comet crashing together – during the solar system’s formation or very soon afterwards when we know those kinds of collisions were common than it is to justify that happening recently, when the solar system is fairly well behaved.

My Work

I’m not going to discuss in detail my modeling of the ring system. If people are interested, they can e-mail me or post in the Comments asking for a copy of the 15-page paper. But I will give you the basic idea:

Cassini is a craft that’s been in orbit around Saturn since 2004. Besides many truly awe-inspiring pictures it’s taken, an instrument on it also performs stellar occultation measurements through Saturn’s rings. Over the course of nearly 6 years and well over 100 such observations, we have a much more detailed understanding of the optical thickness of the rings — how difficult it is for light to get through any given location in the rings as a distance from Saturn.

For my research, I performed what are called N-body simulations, where in the computer I created a mini saturnian ring section. I varied many different properties – including the ones I mentioned a few paragraphs ago – and I let the system evolve from an initially random state. I then simulated a Cassini observation through my little ring section.

I then compared the results of my simulated occultation to the real ones. From these results, I was able to further narrow-down some of the basic, fundamental properties of the rings. The most important one was that I was able to place a new, minimum mass constraint on the total mass of the ring system. This new constraint is about twice as large as the original one – about 2 times the mass of Saturn’s moon Mimas.

How Does Mass Relate to Age?

Directly, it doesn’t. But indirectly, it does, and I’ll explain here two examples of why.

One is the example that I explained above — if you have more material, then the dynamical lifetime is longer, and you can make the rings correspondingly older by the simple fact that they are still there today to be observed.

A second reason why is that of pollution. As the ring particles orbit Saturn, micrometeorite impactors rain down on the rings and will pollute them. Through various observations and modeling constraints (including mine), we know that the rings are more than 90% water-ice. This is really pure ice and raises the question of how something so old could be so fresh, especially with the pollution from other material.

The answer lies at least partially with the mass: If you have more material there to begin with, then you can more easily “hide” the pollution. For example, if a factory spits out sewage into a small lake, then after a day that lake will look pretty gross. But if that factory spits out the sewage into the ocean, it can do it for many, many years before the ocean is going to show any signs of being polluted. The same is true with the rings.

Hence, as a result of my paper and placing a new minimum mass constraint that’s larger than before, you can push the age of the rings further back in time. And my work is just a minimum estimate — if I had faster computers and more time and weren’t actually doing research on something completely different, then I could push the simulations to many more particles over a larger area and simulate even more massive rings to really try to nail down that mass. But, in 2017 or whenever they choose to kill off Cassini, it will fly between the planet and the rings and we will be able to directly measure the gravitational tug on the craft by the rings and should be able to answer that question. But I digress …

Anticipated YEC Responses

I don’t actually expect YECs to directly respond to my paper in particular. I think it approaches the problem too indirectly for them to take notice and think it’s worth writing about.

What I do expect is for them to respond to the Science article. It’s title is quote low-hanging fruit for the YECs: “An Evolving View of Saturn’s Dynamic Rings.” Wow. They have both “evolving” and “dynamic” in there. I expect that:

(1) Creationists will somehow try to link this to “darwinism” and that an old ring system “belief” is driven by some desire to provide “millions of years” for evolution to occur.

(2) Creationists will have issues with the Copernican Principle and argue that we do live in a specially created time and place where “the heavens declare the glory of God.”

(3) I expect the creationists will key in on the dynamical nature of the rings that we see today. This is not something that I talked about in this post much at all. Very briefly, it has to do with moving from the “granola bar model” to self-gravity wakes of material clumps that we have observed in simulations, theory, and observations that move around, exchange material, and produce bumps, ridges, spokes, and cusps in the rings that Cassini observes. If they do happen to address this, then I’ll discuss it more in my response post.

Final Thoughts

There you have it. I have a prediction out there. I’ve preemptively discussed my own research in this area and hopefully explained it in a reasonably clear way. Now let’s see if the YECs bite.