The science fiction blockbuster "Avatar" is set on a mysterious alien moon with out-of-this-world technologies. Its star director, James Cameron, has not only directed other science fiction epics like "Aliens, The Abyss" and the first two "Terminator" films, but was apparently the president of his high school science club, a physics major in college and has an engineer brother who has designed underwater robots.
So how much science is there in "Avatar"?
CAUTION: Possible spoilers ahead.
The movie is set on the fictional Pandora, one of the many moons of a fictional Saturn-sized gas giant, Polyphemus, which is located in the real Alpha Centauri system, which at nearly 4.4 light-years away is the closest star system to Earth.
While astronomers have yet to discover moons beyond our solar system, they expect to. And the Alpha Centauri system could be a place worth looing. The larger of the two real, sunlike stars that make up this alien system, Alpha Centauri A, is the fictional Pandora's sun. In reality, scientists might soon be able to detect habitable moons with the James Webb Space Telescope and also study their atmospheres for key life-related gases such as oxygen, and water vapor.
Tropical rainforests cover most of Pandora's continents, which suggests its mother planet must be fairly close to its sun to take advantage of its light. A few years ago, this might have seemed implausible, but most of the alien planets scientists have discovered so far are in fact gas giants that are exceedingly close to their stars.
However, life on a gas giant's moon might present a host of challenges. Jupiter's moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field, and Saturn's gravitational pull leads to extraordinary tidal effects that may have once ripped apart nascent moons to produce its rings, and today can drive winds and volcanic eruptions on its moon Titan.
The draw that Pandora has for humans is a naturally occurring ore dubbed "unobtanium," an old in-joke in science fiction for materials with physically impossible qualities. (Technically, since it's a mineral, it might better be called "unobtainite," but that's a pretty nerdy quibble.) Unobtanium is the best superconductor known, and apparently works at room temperature. Just as real-world superconductors can float in the presence of a magnetic field, mountains on Pandora apparently loaded with unobtanium can float in the powerful magnetic pockets that dot the moon's surface. The films show these magnetic fields can interfere with technology, just as they would in real life ? although, apparently, not whatever wireless links which allow the main characters to link with their "avatars."
The devices that give the film its name are avatars ? artificial bodies the main characters operate wirelessly by thought alone. The bodies in question resemble the native blue-skinned humanoid race, the Na'vi, although they are hybrids that incorporate the DNA of their operators.
Building a body that weaves together human and alien DNA might be far-fetched. Even if aliens have DNA, humans would probably have more in common with corn or anything else on Earth than with life on Pandora. Still, scientists in real life are making advance after advance when it comes to brain-computer interfaces to control robot arms and type and speak through machines. Even without brain-computer interfaces, telepresence units are now allowing surgeons to perform life-saving operations from afar.
The humans also operate AMP suits, robotic exoskeletons that mimic their drivers' moves and give them incredible strength to handle giant cannons and fight dinosaur-sized aliens. The U.S. Army has been developing exoskeletons for years to amplify a soldier's strength using combustion engine-driven hydraulics that behave as artificial muscles.
Life is often huge on Pandora, with giant dragon-like flying creatures, skyscraper-high trees, and the blue-skinned Na'vi, who grow some 10 feet tall. The gravity on Pandora is said to be lower than on Earth, which probably helps explain why everything is so outsized there, as they have less weight dragging them down.
Most of the animal life on Pandora is hexapodal ? that is, six-limbed, for three pairs of either arms, legs or wings. One might expect six legs or more to be the norm on higher gravity worlds, to help them support their weight, but hexapods make up more than half of all known living creatures on Earth ? the insects ? so widespread hexapody falls within the realm of possibility.
The Na'vi are tetrapods, or four-limbed just like humans are, which at first makes them stick out like sore thumbs. Still, there are other tetrapods shown in the film ? their flying mounts, the banshees or ikran, possess four wings as their limbs. This might intriguingly suggest the Na'vi are more closely related to these dragon-like animals than any of the land-dwellers shown in the film, although either Na'vi or banshees or both species might in fact come from a hexapodal lineage and merely shed two limbs, just as snakes got rid of their legs.
Apparently every living organism on Pandora is bioluminescent, meaning it can produce light. Bioluminescence is also seen on Earth, with fireflies and sea algae, among others. Many of the animals seem to possess two pairs of eyes ? on Earth, insects not only have a pair of compound eyes, but a number of simple eyes as well.
The 'nostrils' of Pandoran animals are often located on their bodies instead of their faces, and they often have more than two. This suggests that instead of coupling the digestive and respiratory tracts together as humans and other tetrapods do ? which can dangerously lead to choking ? wildlife on Na'vi may separate these systems as insects do, which breath through holes dubbed spiracles.
The biggest stretch of the imagination when it comes to biology on Pandora might actually be the Na'vi. Barring their blue skin and tails, they look remarkably human, with four limbs, nostrils on their face, and an upright posture that might not be aptly suited for a life spent mostly in the trees. The females even have breasts, even though Cameron admits they aren't placental mammals, and we're extraordinarily lucky to find them when they are at a comparable level of intelligence as us ? they might as easily fallen anywhere between animals barely capable of language to hyper-advanced cyborgs.
Still, one might forgive a little poetic license in a film that in other ways apparently tried hard to get the science right might.