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There were a bunch of other things bugging me about Avatar.. Some of my fussing was unfounded.
This had to do with the fun of designing a livable moon that orbits a gas giant. Pandora, or the world I’m working on: Nysus. This has to do with three things: Roche limits, Hill Spheres, and tidal locking.
I’m a biologist, so I actually have to look these up. Fortunately, Wikipedia has the relevant equations, and when I was designing Nysus, I set up simulations in Excel to figure it all out. Right now, based on my memory of the movie, I’m trying to figure out if they got it right.
Here are the issues:
The Roche Limit is the minimum orbital distance where a moon breaks up due to stresses from the gravity of the big planet. That’s where Saturn’s Rings came from. The fun part is that the rigid Roche Limit is based on the densities of both the gas giant and its moon, so on a soft and fluffy gas giant, the rigid Roche Limit’s actually inside the gas giant. While Pandora’s ridiculously close to its primary, it’s outside the Roche Limit, because it’s orbiting a gas giant: Polyphemus.
The Hill Sphere is where the gravity of the gas giant and the gravity of the sun are equal. If a moon’s orbit is outside the Hill Sphere, the sun yanks it away. Pandora doesn’t have this problem.
A moon that’s anywhere near its primary tends to be tidally locked so that one face of the moon always faces the primary. From that moon, the primary basically sits at one point in the sky, never rising or setting.
If you want a 24 hour day on your exomoon, it’s got to orbit its gas giant primary every 24 hours.
One thing I noticed fiddling around is that, while the equations are complicated, things tend to be proportional. If your moon is orbiting a big planet, it goes a little faster, so it’s further away from the planet. Assuming you don’t fiddle with the density of the gas giant, it gets a little bigger, and it so the gas giant appears roughly the same size in the sky.
Now, we get to that fascinating question: how long was Pandora’s day? If it’s 24 hours, Polyphemus covers 25-35% of the sky, not half the sky, which is 90 degrees. If Pandora’s day is 12 hours, Polyphemus covers 40-50 degrees.
Now in the movie, Polyphemus sometimes covers something like 90% of the sky, and sometimes there’s a lot of blue sky showing. This suggests that Pandora actually is spinning, which is not a good thing. If by some weirdness, Pandora actually rotated with respect to Polyphemus, it would have truly godawful tides. How big? I don’t know, but when I calculated them for Nysus (which as about a 48 hour day), the tidal bulge was around five kilometers high. If Polyphemus is rotating, that means the tidal range is several kilometers. As I said, it’s bad. Fortunately, moons get tidally locked pretty fast.
And then we have the issue that the Alpha Centauri system has two stars, not one, and B’s orbit around A is highly elliptical and takes about 80 years to complete (distance varies between 11 and 35 AU, roughly). Therefore, the energy input to Pandora would vary enormously over that time, but it’s more than what Earth experiences. I’m not yet sure whether it’s possible to have a livable planet in this system, but since we only saw one sun, I think it’s safe to say that a real Pandora in the Alpha Centauri system would be weirder than James Cameron imagined. Oh well.
Yes, I’m late. I saw Avatar a bit over a week ago. Not that I’m going to bash James Cameron for the details of the movie. Nor do I think that the Na’vi were, well, what the title says.
I’m more interested in what the movie says about science and scientists.
For one thing, kudos to James Cameron for getting one thing right. Most botanists these days are women, and most of them are extremely competent in a variety of fields. Many even look like Sigourney Weaver, although there is slightly more diversity of skin color among today’s botanists.
Conversely, the old Hollywood trope of Scientist-As-Cannon-Fodder is alive and bleeding. In my checkered career here in southern California, I’ve come to the conclusion that most (not all!) Hollywood types have a fundamental contempt for reality, including some who have made misguided forays into conservation work. Any group that regards reality as good, sacred, or inherently valuable is a second-class citizen in most movies. That’s at best. They are more likely to be cannon fodder, monster bait, or monster spawners. James Cameron is definitely better than this (dude made six documentaries after all), but as I note at the end, the tropes had to be served.
No, what I was interested in was how they made Pandora. It’s a spectacular set, but you know, it was a set. What was missing was, well, evolution. And that got me thinking about how we deal with evolution in our society, and how we get that little cladistics revolution out of the biology departments and into matinee movies and fiction bookshelves.
Before your eyes glaze over, let me ask you: if Pandora actually existed, how would life have evolved on it, especially the Na’vi?
Yes, I know exactly why the Na’vi looked like cat-humans (see the end paragraph). I was trying to figure out how they could have evolved. The other big terrestrial vertebrates (like the direhorse) had six limbs, secondary lung thingies on their chests, four eyes, and two neural internet connections. The flying things like the banshees had four limbs, four eyes, secondary lung thingies on their chests, and two internet connections, and the prolemurs had six limbs (top two fused to the elbow), two eyes, one internet connection, and I didn’t see their chests.
Now, any cladistically-trained biologist would plot those traits on something like an evolutionary tree and start giggling. There’s no easy way they could share a common ancestor. Loss of eyes and limbs, sure, conservation of blue skin as an ancestral trait, fine, but loss of lung openings? Hunh? Does that make sense for highly active arboreal humanoids? Not really. And those neural connections. What kind of evolution drove those connectors, and why do you need fewer if you’re presumably more intelligent. That’s so, well, Apple. I mean, free lifelong internet service, with postmortem archiving in the Wood Wide Web is great and all, but how could it have evolved, and why are the plants and animals using a common internet protocol? The only thing I could think was that it was some sort of fungal infection that affected animal brains and plants as well. But then, I would think that way.
No, the critters of Pandora, fascinating though they are, still look like they came out of an art department. A very well-read art department, but not one that’s familiar with the idea of evolution favoring common body plans and repeated themes of development and evolution.
And that’s what I mean about getting evolution out of the biology departments and into the movies. What would Pandora have looked like if they’d taken an extra few hours and laid out some common evolutionary themes to follow as their design book?
Well, that’s where the title of the piece comes in. Where were the non-Na’vi primates? The prolemurs? That’s it? We needed sky blue cat-monkeys! And what about those secondary lung spiracle thingies? It’s possible to put them on a primate. It would have been possible to put a reduced form on the Na’vi, even. Just put two spiracles on the chest wall, and have their chests bulge heroically as they inhale. You could even explain those superfluous mammaries on the female Na’vi as secondary lung extensions to support the respiration required by carrying a fetus. So, when a female Na’vi inhales, her bust swells by one or two cup sizes. That would have been guaranteed to titillate, no, mesmerize the 16 to 35 year-old male demographic that movie makers reportedly prize. It probably would have annoyed everyone else though.
And that’s kind of the point: James Cameron ain’t stupid, and he managed to persuade investors to cough up $237 million plus to let him make Avatar. To do so, he had to use all the tropes that would be guaranteed to sell movies. Even if he had thought about nipple-breathing Na’vi, they would have been cut, because something that weird and borderline kinky could have damaged Return on Investment. After all, if he got too carried away, there would have been a tense closed-door meeting with investors, followed by a drastically revised script. He had to play it safe. And by playing safe, he’s raking in the loot.
So, the question for us life scientists and others is: so how do you get real science into popular culture? Wouldn’t it be cool if we could actually get people to use evolutionary themes as part of the basic design work? Wouldn’t it be even cooler if creative types were actually praised for incorporating science into their work, instead of just grabbing superficial images?
What do you think? How do we get there from here?
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As I posted on Rick Halsey’s Facebook page recently, I’m looking for an article. I’ll describe the article in a second, but let me first get my soapbox out about the desert solar and wind land rush. Let’s see, where to start:
–I could start with the problem, dating back to pioneer days, that land that has been developed is worth intrinsically more than undeveloped land. No, really. The value is from real or potential water, mineral, etc rights. So Joe Idiot tries to farm the desert, scrapes it bare, goes broke, leaves a useless eyesore, and that’s still worth more than an adjacent area full of endangered plants and animals. I’ve heard rumors that Senator Feinstein is trying to change this provision, and if so, bless her and help her out, because what’s happening is that just about every undeveloped acre of BLM land in the southwestern deserts has a solar or wind plant targeted at it. Not the screwed up areas so much. Just the undeveloped land. Time to scream, environmentalists!
–Or, conversely, I could start with the problem that the local power utilities understand how to build power lines and work with big, monolithic power plants. So they want to build more. In Mexico, even (I think having a big, gas-burning power plant near Tijuana is an excellent way to light up San Diego. Don’t you?). Conversely, the local power companies have issues with dealing with dispersed power generators, like, say, people with solar panels on their roofs. As a result, San Diego just raised the cost of permitting a home solar panel by several hundred percent, while other states (such as Massachusetts) are already implementing programs to buy any surplus power that their customers generate. Time to scream? Sure, why not?
–Or, perhaps, I could start with the problems with utility corridors. They’re ugly, they kill birds and wildlife, and …. Ummm, oh yeah, power lines also start fires. That’s a bit of an ugly problem. We certainly need more fires in southern California (see more from The chaparral institute on this). Powerlines are also vulnerable to fires and earthquakes. And, to get back to the topic of this post, power lines are exquisitely vulnerable to terrorism.
Terrorism? Well, I’m absolutely not interested in taking down a line. However, someone (I seem to recall it was one of the Nixon cabal, possibly G. Gordon Liddy) published this article back in the 1980s. In it, he described, in some detail, how he could use approximately 50 men, some shotguns, dynamite, and similar supplies, to take out the West Coast. His idea was to shoot the wires off the insulators on the high tension lines (that’s what the shotguns were about), dynamite certain key towers and power distribution centers, blow up a couple of aqueducts, and dynamite a few freeway passes through the mountains. Result: people across the West Coast would have no power, no water, and no way to leave except by walking or driving an ORV. Evil man.
Now, to repeat, I have absolutely no desire to follow these instructions. However, I would like to find a copy of that article, mostly so I can include it in EIR/EIS comments on all these damned power lines they want to put in in the next year. It’s stupid to destroy so much undeveloped land and make ourselves more vulnerable at the same time.
While we’re at it, if anyone can figure out a way to reach into Washington and get them to focus on decentralizing the power grid, not just making more huge plants, I’m open to suggestions.
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Welcome! I thought it would be good to have a stump to speak from. The topics here are whatever I feel like speaking about, which is mostly going to be life, life science, living in San Diego, the dubious pleasures of being an environmental-type in the twenty first century, writing, and anything else that takes my fancy. Feel free to comment, but I reserve the right to excise anything I don’t like, particularly spam.
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