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Episode 72: Solar System Mysteries "Solved" by PseudoScience, Part 1 - Iapetus

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Recap: In this first edition of Solar System Mystery Science Theater, we learn about Iapetus, a weird moon of Saturn that has features unlike any other object in the solar system. Some have explained those with exploding planets and spaceships. Others look for something that makes sense.

Puzzler for Episode 72: There was no puzzler for this episode.

Answer to Puzzler from Episode 71: Planetary objects are not perfect spheres with no density deviations whatsoever. You will always have a little bit more mass somewhere on the body. If that object is close enough to another, more massive object, then that more massive object will tug a bit more on that extra mass every single time it rotates closer to the more massive object. Like if you have a perfect sphere except for one big mountain on Earth, then every time that mountain is aimed towards the Sun, it's going to pull just a teensy bit more. And, over a very long time, that all adds up to slow the rotation until that extra bit of mass is facing the more massive object. Since gravity is an inverse-square law, this means that if your two objects are close together, then the tidal locking is going to happen much more quickly. That's why Mercury is locked in a 3:2 resonance with the Sun but Mars isn't.

Q&A: There was no Q&A for this episode.

Additional Materials:


Concept: The concept of this series was originated to talk about the Pioneer Anomaly, and I plan to do so in future installments. What I'm aiming for is to talk about a genuine weird thing in the solar system that we didn't have a good explanation for, so people used an argument from ignorance to propose their own pet ideas. That may seem like the idea of the entire podcast program, but I'm trying with this to be more specific.

Claim: For example, in this Part 1 episode, I'm going to talk about Saturn's weird moon, Iapetus. Iapetus has two main very odd features about it and we didn't know for a long time what caused them, and there are still competing models for one of them. In that gap of knowledge entered both Exploding Planet people and the venerable Richard C. Hoagland, offering to fill these holes with their own oddly shaped tools.

Exploded Planet Overview

Just over a year ago, I did a two-part episode on whether the asteroid belt could be the result of a planet that exploded a very long time ago. I'm not going to rehash all of that information now, but the basic idea is that a large planet orbited where the asteroid belt currently is, it had several moons including what we now have as the planet Mars, and that it exploded. This created the asteroid belt and several other anomalies across the solar system that they claim is best explained by a planet that exploded.

Not to jump the gun too much, but the problem with saying that these things are best explained by a planet that exploded is that planets don't explode, and the evidence pointed to for this happening is sketchy at best. And that the many lines of evidence are wrong. Go back to episodes 29 and 30 for more on that.

Iapetus Albedo Differences

One of the mysteries that I touched on in episode 30 is Saturn's moon Iapetus. If you do an internet search for "Iapetus exploded planet," the first link is for a remote viewing website where they claim to have had their remote viewers test whether the exploded planet model or an actual science model really happened. Amazingly, the remote viewers came down on the side of the exploding planet model. I was shock-ed. But what are they trying to explain?

Iapetus is a weird moon. As far back as the 1800s, we knew that it had one side that was really bright and one side that was really dark. This was figured out just by watching how its brightness changed over the course of several nights as it rotated. Incidentally, this is also how we can measure how fast asteroids that we can only see as a single pixel actually rotate: We watch how their brightness changes and look for periodic behavior, and each repeating cycle is one new rotation.

Getting back to Iapetus, one half dark, one half bright. The first photos returned by the Voyager space probes emphasized this even more, where one part is darker than fresh asphalt, reflecting only 3-5% of the light that reaches it, while the other part is almost as bright as fresh snow, reflecting about 50-60% of the light that hits it.

The dichotomy is such that the leading hemisphere is the one that's darker, while the trailing one is brighter. Iapetus has a leading and trailing hemisphere because, just like our moon around Earth, it's tidally locked to Saturn, always showing the same side to it.

The mystery is what formed this brightness dichotomy.

I've read a few different versions of the solution via the exploded planet hypothesis. The general one that makes the most sense is that Iapetus was hit by a particularly strong blast wave of material from the exploded planet, blasting one part of one side and forming the dichotomy. Otherwise, you just have the generic, "Material from the exploded planet hit Iapetus and it got dark on one side." Richard Hoagland added to this by claiming that most other moons are active in some way and so have been resurfaced since the blast.

The problem is this really doesn't work. There was a paper out late last year - a very long paper - about the origin of the grooves on Mars' moon Phobos. Don't worry -- there is a connection here. The best explanation for the grooves was that a large crater formed on Mars and threw material up into orbit, and that material formed the grooves on Phobos when the moon plowed through it. This paper's first author was an engineer and he did the math showing that the debris launched from a crater forming on Mars would have to travel with better precision than our best guided missiles in order to make the grooves on Phobos the way they are. His conclusion was that this isn't possible.

The connection here is that Iapetus is about 7 times the Earth-Sun distance from the asteroid belt, where this "Planet V" would have been. How you could possibly target Iapetus with a debris cloud from a planet that's exploding and hit Iapetus and only part of Iapetus and nothing else from over 1 billion kilometers away is not possible.

So you go to something else: Maybe it hit everything. Problem there is that Iapetus is the only moon that shows this brightness difference.

And so we have Hoagland's modification that Iapetus and other moons were hit, but Iapetus just hasn't been resurfaced like other moons. Problem with this is there are literally dozens of other moons around Saturn with older or similarly aged surfaces to Iapetus and none of them show the same brightness difference that Iapetus does. In other words, Hoagland is wrong with his major assumption that other moons have been resurfaced so removed evidence of this event.

This brings us to what is really going on. This mystery was pretty much solved with the Cassini mission at Saturn within the past decade. The model is a bit complicated, so bear with me:

Iapetus has the slowest day rotation of any moon in the Saturnian system. This means that parts in sun will heat up more than the parts of other moons exposed to sun because they're exposed longer. It also means that the parts on the night side will get colder than the night side of other moons.

The moon was probably originally covered in an icy material, much like most of the other moons.

Dark dusty material blasted off of moons in the system orbited around Saturn and some were eventually deposited preferentially on the apex side of the moon, the one that faces forward in the moon's orbit around Saturn. The dark material is red in color, and the next-moon in from Iapetus is Hyperion, which is unusually red.

Once the material is deposited, it's darker, so it's going to heat up more than the brighter ice. When it heats up, ice underneath it will sublimate, meaning it goes directly from a solid to a gas. It will still be somewhat gravitationally bound to the moon, at least for a little bit, and if the water-gas moves over a part of Iapetus that's experiencing night, then it can freeze out and be re-deposited.

You're still going to get ice sublimation from the parts of the moon that aren't covered by the darker material, but it's a MUCH slower process. Simple thermal models estimate that over 1 billion years at current temperatures, the dark areas would lose 20 meters of ice, but the bright areas would lose just 0.5% of that, about 10 centimeters, or about 4 inches.

As more ice sublimates away from where the dark parts are, they're going to get even darker, and as ice is freshly deposited, the bright parts are going to get brighter. This creates a positive feedback loop so that the process self-perpetuates, especially as Iapetus continues to accumulate bits of darker material preferentially on that leading side.

This model is supported by observations of the areas near the boundary between bright and dark. Crater walls that face Iapetus' poles, which would get the least sunlight of that leading side, have bits of bright material while all the rest of the crater is dark. Also, the dark material is very thin, probably only about a foot thick, or about 30 cm, which is supported both by radar imaging and that very small craters punch through it into brighter ice underneath. This supports the idea that the dark material was deposited on top of the brighter material.

Now, as I said, this may seem a bit complicated versus the simple "a planet exploded and painted on side black." But it's much more plausible. It works with physical and dynamical models. It's supported by the observations. Meanwhile, the exploded planet idea isn't, and predictions made by it, such as an entire hemisphere of Iapetus would be black, are not supported -- it's actually a broad ellipse on one side that's dark.

Iapetus Ridge

Next, we get to Iapetus' equatorial ridge. This is something wholly Hoagland.

Besides Iapetus' weird brightness differences, we have another weird anomaly on this little moon: It has a belt that was only discovered in 2004 by Cassini. Circling its equator is a ridge, and ridge is in the dark area of the moon; there are some isolated peaks up to about half the size of the ridge in the bright areas. The mountain ridge is over 20 km (12 miles) tall which makes it the tallest ridge relative to the object size in the solar system. Nearly the tallest in the solar system as-is, but Olympus Mons on Mars is a bit taller. Iapetus used to be called the "yin-yang" moon due to the brightness differences. These days, the name has changed to the "walnut" moon because of the ridge right at the equator.

As the biggest or smallest or weirdest "something," you know that this is bound to attract some weird ideas. And this one really is weird.

Richard Hoagland published a six-part very lengthy very rambling series on his website back in 2005 about this moon, mostly about the equatorial ridge. And I read it ... or at least skimmed most of it. In typical Hoagland manner, he also blew up highly compressed images and pointed out all the squareness and lines, then did some numerology, and said this was evidence of artificiality. There are numerous things I could talk about, but I promised I'd be focusing on the ridge.

Richard calls it "The Wall" and thinks it was built by an alien race. He argues that the entire moon was built by an alien race from another solar system and "parked" in orbit around Saturn while they went to Mars. He continues, stating that "The Wall" is part of the propulsion system for the massive alien spaceship. In fact, he ends part 6 by "asking the question" of whether this "wall" is "an Einstein UFT [Unified Field Theory] Field Propulsion System?!"

He says that it is only visible on the dark part because it's covered up by debris elsewhere and has been excavated here. That, of course, would mean that Iapetus has over 20 kilometers of burial material that has only been excavated on the leading side, and that ice covers it on the trailing side. As I already discussed, this is wrong because the dark material is on top of the ice, not the other way around as Hoagland thought.

I don't think I really need to go into why this is crazy. I kinda hinted on it with the fact that he's wrong about what's on top of what, his use of bad data, numerology, and other things. And that the bright part of Iapetus is not 20 km higher up than the dark part.

But what really is going on? As I mentioned, this was only discovered about 10 years ago, and it's very weird. There are a couple actual science ideas as to why this exists, though some are more likely than others.

1. Leading with the least likely explanation is that Iapetus had a ring system early in its history, and this ring collapsed onto the surface. The reason why this isn't likely is that the ridge seems to be too solid to just be made of particulate material from a ring. It's covered with craters, has tectonics running through it, and so it would be hard for this to be from a collapsed ring.

2. Another idea is that very early in its history, Iapetus had enough heat to be convective, and that lighter material concentrated near the equator due to Coriolis forces and this formed the bulge. Not sure how likely that one is.

3. Another endogenic idea, meaning that it came from Iapetus itself, is that icy material welled up from beneath its surface and then solidified when exposed to space. It may or may not have formed at the equator, but over time, Iapetus would slowly rotate until it IS at the equator because that's the minimum energy configuration. Incidentally, this is also probably why the giant basins on Vesta are at the pole, and why the giant volcanic region of Mars is at the equator. Probably didn't form there, but the planet rotated that way over hundreds of millions of years because of tiny gravitational tugs from other bodies in the solar system torquing it so mass loads are at the equator and deficits are at the poles.

4. A fourth model is that the young Iapetus rotated much more quickly than it does today -- instead of once every 79 days like it does now, it rotated once every 17 hours. The rapid rotation would have caused material to bulge out at the equator while Iapetus was still warm enough to be deformed, and as it cooled, the ridge froze into place. The spin slowed down as tidal forces acted on the moon to eventually lock it into its current slow, 79-day rotation, just as our moon is locked into a slow rotation as it orbits Earth.

The problem with all of these is that they invoke physics that not everyone knows about, and with limited data, it's hard to rule one as better than the others. On the other hand, everyone knows about spaceships and Star Trek and it's much easier to look at crappy photos and not realize that you're seeing artifacts in the images. I think that's why Richard is able to have at least some people believe him, while it's harder to get people to understand the actual science of what's more likely to be going on.

With that in mind, this first edition of Solar System Mysteries that were PseudoSolved is wrapped up.

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