Icy flakes are all in a day's work for Caltech physicist

PASADENA, Calif. -- Ken Libbrecht is perhaps the flakiest man in the rarified world of physics.

Working in a small laboratory at the California Institute of Technology, Libbrecht routinely matches Mother Nature's skill in churning out a product as beautiful as it is ephemeral: the snowflake.

Snow-crystal growing can be accomplished in minutes, if not seconds, making it a nice change of pace from Libbrecht's other pursuit, the search for gravity waves. The elusive, theoretical ripples in the fabric of space and time have eluded scientists since Einstein's day.

"There is a lot of instant gratification," Libbrecht said as he adeptly demonstrated his snowflake-making technique, cranking out multiple crystals, each as unique as any found cascading from a cold, winter sky.

Libbrecht, chairman of the university's physics department, began studying snow crystals -- snowflakes are actually clumps of snow crystals -- about five years ago.

The results are stunning: His Web page contains countless images of snow crystals. He and photographer Patricia Rasmussen plan a book to feature the most photogenic crystals they've spied in nature and created in the lab. But the work is also valuable science.

"I just became intrigued by the physics and that we don't understand how it works -- how ice crystals grow," said Libbrecht, whose upbringing on a North Dakota farm gives him an impeccable cold-weather pedigree.

A dynamic life

Scientists know that snow crystals form from water condensed from its gaseous state, each growing around a tiny nucleus, typically a speck of dust.

As more and more molecules attach to the growing crystal, they do so selectively, giving it its distinctive, hexagonal shape. Libbrecht said crystals are like human faces. Stand back far enough, he said, and any two appear identical. Come closer, though, and their variety shines through.

Each tiny crystal has a dynamic life as it totters on the brink of the melting point.

"Thermodynamically, it's an extraordinarily active material, so it's always changing," said Sam Colbeck, a retired geophysicist from the U.S. Army's Cold Regions Research and Engineering Laboratory in Hanover, N.H., where he studied how crystals grow in snow cover.

Not a crowded field

Libbrecht has developed the means to study crystals firsthand, even on winter days when the Pasadena campus of Caltech basks in sunshine.

He is one of perhaps a handful of physicists and meteorologists who work in the field -- and that's fine by him.

"I've worked in fields that are crowded before, and I prefer not to," Libbrecht said.

Libbrecht grows his crystals in a small, insulated box made of plastic foam and glass, sealed with silicone caulk. The box is cooled at the bottom and heated at the top, creating within a stable temperature gradient. A piece of felt, soaked in water, creates moist air from which growing crystals snag water molecules.

A piece of two-pound test line is stretched across the various gradients. Crystals grow fastest at the point on the line where conditions are just right.

"It's not toxic or messy. And it's cheap," Libbrecht said.

Libbrecht showed off three clumps of crystals, spaced fairly evenly along the line. The distribution illustrates how temperature-sensitive they can be.

At 28 degrees Fahrenheit, the crystals grow as plates. At 23 degrees, it's columns or needles. At 5, it's back to plates. If temperatures dip as low as minus 20, it's columns again.

"It sort of varies, plates to columns to plates to columns to plates, as a factor of temperature," Libbrecht said.

Crystal needles

Replace the string with tungsten wire and the story becomes even more dramatic.

Libbrecht first puts 2,000 volts of electricity through wire. That creates an electrical field at the tips of ice crystals already present and encourages them to grow further.

Magnified by microscope, the crystals can be seen to surge in length, growing 10 times faster than normal to form slender, hexagonal "pencils" of ice.

"They just shoot out in long, thin needles," Libbrecht said.

Cutting the voltage and dropping the temperature, the crystals revert to more normal growth patterns.

It takes Libbrecht just a few minutes to grow flowers of ice, complete with delicate crystals sprouting from the stalklike columns. "Designer crystals," he calls them.

On a recent morning, one of the stalks of a just-grown example began to droop, dropping into view a perfect, star-shaped crystal.

"Oh, look at that. It doesn't get any better than that," Libbrecht said.