The Science of Avatar

by Stephen Baxter

  It seems remarkable that even a toy magnet is so much stronger than Earth’s magnetic field—and, if you use one to pick up a pin, you will witness its magnetism overcoming the gravity pull of an entire planet. But you have to think of magnetic field strength as a kind of density; there’s an enormous amount of energy stored in Earth’s field, which works globally—even if locally, on a very small scale, it is much weaker than the fridge magnet. And on larger scales, whereas electrical and magnetic forces can attract or repel (think of positive and negative charges, north and south poles) gravity only ever attracts. So electromagnetic forces can be strong on short scales but cancel out on larger scales, whereas the attractive force of gravity just piles up and up. That’s why the structure of your body is dominated by electromagnetic forces, but the structure of the universe, such as the orbits of planets and the spiral forms of galaxies, is determined by gravity, not electromagnetism.

  Selfridge’s toy is one thing. What about the Hallelujah Mountains?

  Just as I imagined a biologist as a cylinder (Chapter 14), now imagine a mountain as a cube, a hundred metres on a side (many of the mountains are a lot larger), with the density of rock. This is a lot more mass than the desk ornament—around two million tonnes—and the pressure needed to keep it up is much greater too, at around one million, six hundred thousand pascals. And the magnetic field strength we need is greater too, around a couple of teslas.

  A couple of teslas might not sound much. It’s well within what modern human technology can produce—the big magnetic resonance imaging systems in hospitals can run up to fields of several teslas, on a small scale.

  But this is several thousand times Earth’s field strength. It’s stronger than the magnetic field around Jupiter. It’s stronger even than the sun’s field at the location of a solar flare, an event powerful enough to batter the Earth across more than a hundred million kilometres with enough charged particles to crash power grids. But there are stronger magnetic fields in nature; the field at the surface of a neutron star, a compressed supernova remnant of the kind that created unobtanium in the first place, can run to hundreds of millions of teslas. (Robert L. Forward’s novel Dragon’s Egg (1980) and my own Flux (1993) showed life forms shaped by this bizarre environment.)

  In the movie Avatar we see visual evidence of strong magnetic fields of a poetic sort. The Stone Arches that congregate over areas of strong flux, such as the Tree of Souls, are reminiscent of “solar prominences,” areas of intense magnetic activity on the surface of the sun where glowing plasma is lifted along flux lines to form tremendous arches—some big enough to straddle the Earth. The Arches are in fact a relic of Pandora’s magnetic fields. During the region’s formation flux loops shaped the rock when it was still molten, and held it there until it cooled and hardened. As a result arch formations can be used to locate unobtanium deposits, and act as warnings for pilots of aircraft of the presence of hazardous magnetic fields.

  Regarding the flying mountains, even if you had the field strength, there are also questions of stability. If you experiment with fridge magnets you’ll find that supporting an object by repulsion isn’t so easy, as the object will slide off to one side or another, or flip over so that unlike poles are drawn together. With a superconducting body the effect is different, as the floating body is cushioned by the magnetic field excluded from its interior. Maglev experiments have shown that for stability you need the supporting field to be stronger at its periphery than at its centre, to keep the floating object in place. On Pandora, how could such a shaped field come about in nature? Perhaps there was some kind of feedback effect between the magnetic fields in the floating rocks and the still-molten ground, when the mountains were formed. Or, some researchers in the Avatar universe have speculated, the Hallelujahs could represent a balance achieved by a kind of consciousness, just as Eywa is integral to the balance of the ecology… Even so the Hallelujahs aren’t entirely stable, however. They have been known to collide, hence the Na’vi name for them of “Thundering Rocks”: tktktk.

  Certainly Pandora’s intense magnetic fields will add to the hazards of a very hazardous world.

  17

  A DANGEROUS MOON

  Colonel Quaritch likes to welcome newcomers to Pandora with a scary depiction of its dangerous life forms, the plants, the animals, the natives, all of which, according to him, want nothing more than to kill humans.

  But Pandora would be a ferociously hazardous place even without any life forms at all.

  Pandora is a volcanic world. And it’s that way because of where it orbits.

  Consider the moons of Jupiter. Of the four largest moons, discovered by Galileo—Io, Europa, Ganymede and Callisto—closest-in Io is some six Jupiter radiuses from the giant planet’s centre, while furthest-out Callisto is about twenty-six radiuses out. Io has had its orbit tweaked into an ellipse by its neighbours, Europa and Ganymede. As a result Jupiter and the neighbouring moons together raise ferocious tides on Io—and not of water, as our moon raises tides in Earth’s oceans, but of rock. The whole moon is flexed and squeezed, an effect that heats Io from within, just as a rubber ball gets hot if you knead it in your grip. It’s just the same for Pandora, which too orbits a gas giant and has sister moons, so we must expect it to suffer similar tidal flexing.

  Because of the heat injected by gravitational kneading, Io is the most volcanic world known. Its calderas spew out a hundred times as much lava as from all of Earth’s volcanoes—and that from a surface area just one-twelfth the size. The whole surface is riddled with sulphurous pits, lava pools and magma-spewing fissures. In NASA spacecraft images Io looks like nothing so much as a vast plate of pizza. This is unusual for a small world. Smaller planets lose their inner heat more quickly, and tectonic activity generally seizes up; that’s the case on the moon and even on Mars. Not on Io—and not on Pandora.

  Clearly Pandora is not such an active world as this. But it is an arena of much more intense tectonic activity than Earth: a world of fractured continents, of volcanoes and earthquakes, of hot springs and geysers, and with its air polluted by carbon dioxide, hydrogen sulphide and other volcanic products.

  All the volcanism is bad for machinery, because of the ash and gases volcanoes inject into the air. On Earth we had an example of this in April 2010, when air travel across north Europe was closed for days because of an ash cloud emitted by a volcano in Iceland. The eruption wasn’t that big by historic standards, and away from Iceland itself you couldn’t even see the cloud. But an airliner flying through it would ingest sixty billion particles of abrasive ash every second. The worst danger was that particles of silica in the ash would melt and clog up the engines’ cooling systems, which was likely to shut down all the aircraft’s engines at once, rather than one or two dropouts which airliners are designed to handle. Pandora is evidently a tough environment for industry, as we’ll discuss in Chapter 18.

  As for humans, the Pandoran air is lethal. “Exopacks on!” barks the crew chief as the Valkyrie passengers prepare to walk on Pandora for the first time. “Remember people, you lose your mask you’re unconscious in twenty seconds and you’re dead in four minutes. Let’s nobody be dead today, it looks bad on my report…”

  Thanks to the volcanism, compared to Earth’s atmosphere, Pandoran thick air is stuffed with carbon dioxide, xenon and hydrogen sulphide. It’s the carbon dioxide that keeps the moon warm enough for life. But it’s the carbon dioxide that would kill you—or the hydrogen sulphide, if you gave it a chance. (The xenon is harmless.)

  Carbon dioxide is an essential component of our biosphere, but it is toxic in greater concentrations: a silent, odourless assassin. In 1988 in Cameroon, carbon dioxide was expelled from lakes by volcanic events; animals in the area were overwhelmed and killed, as were seventeen hundred people. Coal miners are wary of “blackdamp” in their mine shafts, toxic air in which raised carbon dioxide levels are matched by reduced oxygen. It was to warn of the dangers of blackdamp that canaries were used as a warning system; t
he birds, more sensitive to bad air than humans, would succumb first.

  The carbon dioxide content of Earth’s air is around a fraction of one per cent. From one per cent upwards it can cause drowsiness. At higher concentrations you get dizziness, shortness of breath, difficulty breathing and panic attacks. At eight per cent you lose consciousness after a few minutes. On Pandora, the concentration is nineteen per cent… After Quaritch’s climactic attack with his AMP suit on the link shack, Jake is left exposed to Pandoran air without an exopack, and his rapid near-suffocation is convincing.

  Pandora’s high concentration of hydrogen sulphide is a hazard too. This gas is deadly at concentrations of more than a few tenths of a per cent, but capable of causing coughing and skin irritation at much lower levels.

  Of course Pandoran life forms are adapted to their air. There is even one sort, the “puffball tree” (Obesus rotundus) which absorbs toxic gases from the atmosphere, for the benefit of the rest of the ecology. Humans, however, will always need protection from systems like their exopacks, which remove the excess carbon dioxide and hydrogen sulphide from a user’s air.

  If Pandora’s air doesn’t get you, meanwhile, there’s the magnetism.

  Pandora’s own magnetic field is hazardous enough. Locally, as we see onscreen, it is strong enough to affect human technology—which is why regions of intense flux, like the Tree of Souls, are good places for Grace, Jake and the rebels to hide out. As we will see in Chapter 18, one reason why much of RDA’s technology has a heavy, retro look is simply that it has to be robust enough to keep working in Pandora’s intense magnetic environment, amid other hazards.

  The magnetic field would also have an effect on living things. Conceivably you would feel the presence of a strong local field if you walked through it. You’ll recall that unobtanium is pushed away by magnetic fields because as a superconductor it has “perfect diamagnetism”—a chunk of it expels magnetic fields from its interior. But to some extent any conductor is diamagnetic, such as your own water-filled body, and can be pushed by a strong enough field. The bodies of frogs and mice can be made to float in magnetic fields, as has been proven by certain researchers with too much time on their hands.

  Magnetism has more subtle influences. Life on Earth routinely exploits the planet’s magnetic field. Creatures with internal magnetic “compasses,” which get directional information from the way the field is pointing, include birds, sea turtles, bats, lobsters and newts. Some, including turtles and newts, are thought to have internal magnetic “maps” based on three-dimensional variations of the field. Such animals may “see” aspects of the field superimposed over a more normal visual view of the world, like a pilot’s head-up display. Obviously such senses are useful for migratory species of birds, but “magnetoreception” is widespread beyond that, in non-migratory species such as flies and chickens. Even cows in a field can sometimes be seen to line up with magnetic field directions.

  It’s been difficult to identify the receptors for these senses because magnetic fields pass through flesh and blood; an animal’s magnetic sensors could be located anywhere in the body, not necessarily on the surface, the way eyes are. It’s not even clear how magnetic senses work: perhaps through magnetic fields causing a voltage within the body, or through their tugging at a magnetic mineral called magnetite within the body, or perhaps through the fields causing some unusual biochemical reaction within the body. A recent review of the subject in Nature (22 April 2010) summed this up as “a fascinating interplay of biology, chemistry and physics.”

  Magnetic-sensitive life forms used to Earth’s gentler fields would probably suffer on Pandora. This has been demonstrated by researchers placing standard bar magnets, much stronger than Earth’s field, on homing pigeons and sea turtles, whose ability to navigate is disrupted. However, native life forms exploit Pandora’s strong magnetic fields for other purposes than direction-finding (see Chapter 21). Life is endlessly ingenious in exploiting the resources offered by its environment.

  For humans, the medical effects of long-term exposure to powerful magnetic fields are not well understood. But human workers are now routinely exposed to Pandora-sized fields of several teslas, for instance from working with magnetic resonance imaging scanners in hospitals. In 2007 the European Union’s Health and Consumer Protection department published a study of the “possible effects of electromagnetic fields on human health.” The report pointed out that strong magnetic fields affect biological molecules with magnetic properties such as haemoglobin, and there has been some evidence that the electrical activity of neurons and brain areas can be affected by intense fields.

  Pity RDA’s miners. Unobtanium mines tend to be located in the most intense regions of magnetic flux. In fact humans aren’t allowed anywhere near unobtanium deposits; symptoms such as vision distortions and strange tactile sensations are reported hundreds of metres away, along with irregular heartbeats, muscle tremors, nausea and other symptoms. RDA’s mining operations are perforce run by remote control.

  Those flying mountains are another hazard for the miners. If you dig out unobtanium in the wrong place you could destabilise the magnetic fields holding up a Hallelujah…

  So Pandora’s magnetic field is hazardous enough. Its interaction with Polyphemus’ field only makes things worse.

  Jupiter’s magnetic field is ten times the strength of Earth’s. As a result the giant planet is surrounded by a powerful “magnetosphere,” a region of space filled with high-energy charged particles. This magnetosphere extends between fifty and a hundred planetary radiuses, well beyond the orbit of Callisto. This is a big structure; if it was a visible object, from Earth it would look the size of the sun. Inside the magnetosphere there are Van Allen radiation belts, bands of trapped charged particles of the kind known to be a hazard for astronauts orbiting Earth—but Jupiter’s belts are ten thousand times as intense as those around Earth. The magnetosphere has visible effects on Jupiter itself, such as tremendous auroras, caused by charged particles battering the planet’s upper atmosphere: fantastic light displays some sixty times brighter than the northern and southern lights on Earth. And the magnetosphere causes Jupiter to emit huge blares at radio frequencies, more intense than any radio source in the solar system save the sun. Io and the other big moons are all well within Jupiter’s magnetosphere.

  The situation is similar at Polyphemus, whose magnetosphere envelops six of its moons, including Pandora. The interaction of Polyphemus’ magnetosphere with Pandora’s is complicated and interesting. The localised magnetic “hot spots” on Pandora’s surface funnel charged particles from Polyphemus’ magnetosphere or from the sun down to the surface. The result is storms from space similar to those on Earth caused by solar flares, violent releases of energetic particles from magnetically active regions on the sun’s surface. On Earth, extreme events can crash power lines, interfere with communications between planes and ground controllers, and affect mobile phone services.

  But our own magnetosphere is basically a shield. It generally deflects the worst of the solar storms, pushing aside the charged particle flows. Pandora’s complex magnetosphere actually delivers the storms to the surface. An intense enough storm could be lethal for life forms; in the very worst case death could come instantly as the brain’s tissue is ionised, and you just “short out.”

  Another remarkable feature Pandora shares with Io is a flux tube. Io is connected to its parent Jupiter by a tremendous trail of plasma, a natural conductor that carries a current of five million amps across a potential difference of hundreds of thousands of volts, with a power seventy times more than all of Earth’s generating capacity. This astounding structure pours additional heat energy down onto Io’s roiling surface. Pandora’s flux tube is more intermittent, but when it works it creates massive electrical storms, auroras, and other phenomena.

  Quaritch is right. Pandora is a very hazardous world.

  But RDA is on Pandora despite the hazards. The wealth to be found under Pandora’s surface mak
es it worth braving the hazards. And RDA is very efficient at extracting that wealth.

  PART FIVE

  HELL’S GATE

  “This is why we’re here. Unobtanium. Because this little grey rock sells for twenty million a kilo. No other reason.”

  —Parker Selfridge

  18

  DISTURBING THE WORLD

  Among Avatar’s many striking images are aerial views of RDA’s great unobtanium mine on Pandora. It looks like a lunar landscape cut out of the green, across which giant machines crawl. The sheer scale of all this is brought home to us in Jake’s first scenes on Pandora, when, fresh off the Valkyrie shuttle from orbit, he is tiny beside dump trucks, their wheels taller than a standing human—but in other shots we see how the trucks themselves are dwarfed beside the tremendous excavators in the pit.

  The size of an RDA excavator, a DD40 Heavy Duty Class Wheel Loader, is staggering. You could fit seventeen soccer pitches on its mighty back. At five hundred metres long, it is over a hundred metres longer than the largest ships currently operating on Earth’s oceans (Maersk E-class container vessels). And it’s over three hundred metres high: there are only about fifty taller skyscrapers in the world today. An excavator is a single machine the size of a city block.

  There is something awesome in the sight of huge, single-purpose engines like these. As a boy in the 1960s I was struck by the futuristic machines in Gerry Anderson’s Thunderbirds, such as the Crablogger in the episode “Path of Destruction,” which crashes through the jungle pulling out trees with its gigantic claws like a child pulling up blades of grass. Even today I can’t help but be awed when I glimpse the machines that clear-cut the big managed pine forests close to my home in northern England. A “harvester” will fell a tree with its chainsaw, rollers force the tree stem between “delimbing knives” that strip the trunk of its branches, and logs are cut to a specified length. A huge twenty-year-old tree can be processed in minutes. Later a “forwarder” picks up the logs to carry them to great heaps by the roadside for collection. There are humans in the cabs of these machines, but not a lumberjack’s foot touches the ground. It’s not quite the gigantic slash-cutter we see in Avatar, but the principle isn’t far away.