Stephen Baxter - The Science of Avatar

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; the 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.