The Case of the Six-Legged Direhorses

September 2011 Silmarien Szilagyi

I’m sure by now many of you have seen the movie Avatar. If you succeeded in ignoring the frenzy, or have been living in a cave for the past year, here’s a quick summary. On an Earth-like moon named Pandora, a species of humanoid beings called Na’vi live in harmony with their biologically-rich environment. Until humans enter the scene. For the most part, James Cameron and his team are accurate with their science. But there are a few scientific hiccups that I will address in this article. After all, critiquing the science in movies is what this column is all about.

Let’s begin with the world itself: Pandora, one of Polyphemus’s moons in the Alpha Centauri system. Pandora appears remarkably like Earth; there are lush green forests, a blue sky, and familiar animals. However, the similarities are superficial. The visiting humans cannot breathe Pandora’s air because it contains lethal amounts of carbon dioxide (18%) and hydrogen sulfide (1%, though.1% is enough to cause serious damage). As a result, they wear air masks when outside, except, apparently, when flying in an open helicopter. The pilots should wear air masks, or else they’d be unconscious in seconds and dead within minutes. Yet there are no helicopters spiraling out of control, no slumped over pilots. So either these pilots are superhuman, or James Cameron et all blundered. I’m more inclined to believe the latter.

Next are the Hallelujah or Floating Mountains (Ayram alusing in Na’vi), aptly named since they’re huge islands, which used to be outcroppings, that float high above the ground. Waterfalls spill over the edge of many of them, as well. The question on everyone’s minds, I’m sure, is how on Earth do they float? Surely James Cameron’s imagination has finally run away with him? Not so. The Floating Mountains owe their trick to the Meissner Effect. Due to the Meissner Effect, metallic things can float because a magnetic field is ejected when a conductor becomes a superconductor—a cooled, infinite conductor. Put simply, the islands float because they contain a metallic substance called unobtanium, which is pulled from the ground into magnetic currents, taking the islands along for the ride. The same effect has been demonstrated successfully on Earth, though on a much smaller scale; scientists were able to make a magnet float above a superconductor. As with most things in movies, the Hallelujah Mountains are an exaggerated concept based in scientific fact. It’s simply not plausible for huge tons of rock to float, not on a world of Pandora’s size. Pandora is smaller than Earth, which means its magnetic field is weaker than Earth’s. On the other hand, Pandora orbits a gas giant (think Jupter), which may have a very strong magnetic field, and it could reach Pandora, thus bolstering Pandora’s own field. This remains an intriguing concept.

Finally, we reach the fauna. There are dog-like, cat-like, lizard-like, and horse-like creatures. I’ll focus on the last two. The Ikran look like flying lizards, but their metabolism is more bird-like. They have gill slits called spiracles through which Ikran breathe and release excess heat. So instead of inhaling and exhaling through their mouth or nose, they do so through their spiracles. Ikran also have four eyes, two on each side of the head. The first is called the primary eye and is larger than the second, the secondary eye. It’s assumed that four eyes aid in hunting and safety.

However, the Ikran are not the only creature with spiracles and four eyes. A horse-like animal called the Direhorse also possesses these, in addition to six legs. Yes, six legs. But I’ll get to that in a minute. For both the Ikran and Direhorse, spiracles and an extra pair of eyes are beneficial and might even be evolutionarily logical, if the other animals, including the Na’vi, has them. But they don’t. The others have two eyes and no gill slits, though it’s possible to liken spiracles to pharyngeal gills in Earth animals. Most fetal animals on Earth, including humans, begin with pharyngeal gills—premature gills in the neck—in the early stages of development. Perhaps on Pandora, spiracles stuck, but unless they are in all land creatures, the concept is flawed. The same goes for four eyes; other animals hunt and scout for predators, but they do just fine with two eyes.

And now for the grand finale, the case of the six-legged Direhorses. They are mammals, or what would be our equivalent of mammals, just like many of the other Pandoran animals, but only Direhorses have six legs. From an evolutionary standpoint, they are a dead end. On Earth, all mammals have four limbs. All arthropoda (insects) have six or eight limbs. There’s a pattern that can be traced back to the very first aquatic critter that crawled out of the ocean. You can’t just play around with evolution. Also, Direhorses feed primarily on sap and nectar. There aren’t enough flowers on Pandora to sustain a creature the size of an elephant. Horses on Earth graze constantly. It would be impossible to replenish protein, energy, and nutrients from merely sap and nectar. I understand James Cameron strove to be original, but his Direhorses don’t make scientific sense.

Avatar is a science fiction film that does a lot of things right. It’s visually the most stunning movie I’ve ever seen. Its message is even more powerful because we are overexploiting our planet and have decimated our native people. The concept is unique. But all good must be balanced, and even some of the dubious ideas have some scientific merit (except the Direhorses). So give in to the frenzy, crawl out of your cave, and give Avatar a try, if for no other reason than to see the hexapodal horses.