Storm in a Teacup: The Physics of Everyday Life(53)

THE TRANSITION FROM gas to liquid and back again is happening all the time around us. But we don’t see the transition from liquid to solid and back nearly as often. For most metals and plastics, melting happens a long way above everyday temperatures. For smaller molecules like oxygen, methane, and alcohol, melting happens at fantastically low temperatures, the sort of temperatures that require very specialized freezers. Water is an unusual molecule, since it both melts and evaporates at temperatures that occur around us fairly regularly. But when we think of frozen water, we think most often of the North and South Poles of the Earth. They’re cold, white, and forever associated with the great expeditions of the twentieth century that took humans into some of the most inhospitable environments on the planet. Freezing water caused them a lot of problems. But sometimes it also offered unusual solutions.

The transition from gas to liquid is all about molecules getting close enough to each other to touch, while still moving freely enough to flow over each other. The transition from liquid to solid is about the moment those molecules get locked into place. The freezing of water is the most common example of this, but water freezes like almost nothing else. There’s nowhere this weirdness is more visible than the frozen north—the Arctic Ocean.

If you travel to the northernmost part of Norway, stand on the coast, and look still farther north, you see the sea. During the ice-free summer months, the 24-hour daylight nourishes vast mobile forests of tiny ocean plants, a seasonal smorgasbord that attracts fish, whales, and seals. Then, toward the end of the summer, the light starts to disappear. The surface water temperature, which only reached 43°F even at the height of the summer, starts to drop. The water molecules, slipping and sliding over each other, slow down. The water is so salty here that it can get down to 29°F and stay liquid; but one clear dark night, the ice starts to form. Perhaps a flake of ice is blown on to the water, and if the slowest water molecules bump into it, they will stick. But they can’t stick just anywhere. Each new molecule rests at a fixed place relative to the others, and the jumble of bustling molecules is replaced by a crystal, in which well-ordered water molecules are marshaled into a hexagonal lattice. And as the temperature drops further, the ice crystal grows.

The utterly weird thing about water crystals is that the rigorously aligned molecules take up more space now than when they were dashing around in the warm. With almost any other substance, parking molecules on a regular grid would make them sit closer together than when they’re allowed to roam free. But water’s not like that. Our growing crystal is less dense than the water around it, and so it floats. Water expands as it freezes. If it didn’t, the newly frozen ice would sink, and the polar oceans would look very different. But as it is, the temperature drops further, the freezing ice expands, and the ocean grows itself a coat of solid white water.

There are lots of things in the frozen Arctic to get excited about: polar bears and ice and the Northern Lights. But there’s one particular piece of Arctic history that I absolutely love, a story that’s all about the peculiarities of ice freezing, and of working with nature rather than against it. It’s about a bulbous, stout little ship that survived one of the most extraordinary voyages in the history of polar exploration. She’s called the Fram.

Explorers in the late 1800s were drawn to the North Pole. It wasn’t that far away from western civilization. The northern parts of Canada, Greenland, Norway, and Russia had all been visited and at least roughly mapped. But the North Pole itself was a big mystery. Was it land? Sea? No one had ever reached the pole, so no one knew. The voyage defeated explorers again and again because the sea ice grew and shrank and shifted. As weather conditions changed, sea ice could pile up on top of itself, making ridges and ice quakes. The grip of this ice could grind ships to pieces. The USS Jeanette suffered a typical fate in 1881, becoming trapped in sea ice for months just off the northern coast of Siberia. As the weather cooled, and molecules of sea water locked on to the bottom of the ice lattice at the sea surface, the expanding ice gripped the hull. After months of ice growing and shrinking, squeezing then releasing the ship, the USS Jeanette succumbed and was crushed. Explorers who made it off their vessels on to solid ice faced different perils: The ice could melt and open up huge canals, impassable except with a boat. From any of the countries around the Arctic Circle it was hundreds of miles to the Pole, and the shifting ice was a formidable obstacle.

Three years after she sank, unmistakable wreckage from the USS Jeanette washed up near Greenland. It was an astonishing find because the wreckage had crossed the entire Arctic, right from one side to the other. Oceanographers wondered whether there was a current that left the coast of Siberia, traveled across the North Pole, and carried on to Greenland. And a young Norwegian scientist called Fridtjof Nansen had a wild idea. If he could make a ship that would withstand the ice, he could take it to Siberia and freeze it into the ice where the USS Jean- ette had sunk, and maybe three years later he’d pop out in Greenland. But crucially, on the way, he might pass over the top of the North Pole. No trekking, no sailing . . . just let the ice and the wind do the work for you. The only problem would be the wait. Nansen’s reward for this idea was to be both hailed as a genius and derided as a madman. But he was going anyway. He raised the money and employed one of the best naval architects of the age, because the ship itself would have to be like no other ship ever floated on the ocean. And so the Fram was made.