Twin Snowflakes

Growing up in Fargo, North Dakota, Kenneth Libbrecht spent a good part of the year surrounded by snowflakes. Flurries could fall there from October to April. Snow was such a common sight, Libbrecht never paid much attention to it when he was younger.

Libbrecht is now a physicist at the California Institute of Technology in Pasadena. As an adult, he spends a lot of time thinking about snow—even though it’s almost always warm and sunny where he currently lives. Libbrecht is one of the only scientists in the world who studies how snowflakes get their structure. “It’s a fascinating problem,” he says. “Had I looked at snowflakes [as a kid], I would have seen all these intricate shapes.”

Everyone knows that no two snowflakes are alike, right? Not so fast, says Libbrecht. In his lab, he grows his own snowflakes in a custom-built cooling chamber. It allows him to control how each snowflake branches and spreads as it forms. Under the right conditions, he can even create identical snowflakes.

As a kid, Kenneth Libbrecht was surrounded by snowflakes for a good part of the year. He grew up in Fargo, North Dakota. Snow could fall there from October to April. Libbrecht never paid much attention to snow when he was younger. That’s because it was such a common sight.

Libbrecht is now a physicist at the California Institute of Technology in Pasadena. It’s almost always warm and sunny where he lives now. But as an adult, he spends a lot of time thinking about snow. Libbrecht is one of the only scientists in the world who studies how snowflakes get their structure. “It’s a fascinating problem,” he says. “Had I looked at snowflakes [as a kid], I would have seen all these intricate shapes.”

Everyone knows that no two snowflakes are the same, right? Not so fast, says Libbrecht. He grows his own snowflakes in his lab. He has a custom-built cooling chamber. It allows him to control how each snowflake branches and spreads as it forms. He can even create identical snowflakes under the right conditions.

A snowflake begins its life high in Earth’s atmosphere. There, water vapor in the air cools and condenses, changing from a gas to the liquid droplets that form clouds. When clouds get cold enough, some of the liquid droplets begin to freeze into ice. During the freezing process, six water molecules lock together into a hexagon (six-sided shape). This process forms a microscopic ice crystal—a solid whose molecules are arranged in a repeating shape.

Next, molecules of water vapor in the surrounding air bump into the newborn snowflake. They latch on, changing directly from a gas into a solid, and join the growing crystal pattern. This process, known as deposition, repeats, and the snowflake expands. It takes anywhere from 15 minutes to an hour for the snowflake to become heavy enough to fall from the cloud.

A snowflake gets started high in Earth’s atmosphere. There, water vapor in the air cools and condenses. It changes from a gas to the liquid droplets that form clouds. When clouds get cold enough, some of the liquid droplets begin to freeze into ice. As they freeze, six water molecules lock together into a hexagon (six-sided shape). This process forms a microscopic ice crystal. That’s a solid with molecules arranged in a repeating shape.

Molecules of water vapor are in the surrounding air. They bump into the new snowflake and hold on. They change directly from a gas into a solid and join the growing crystal pattern. This process is known as deposition. It repeats, and the snowflake grows. When the snowflake gets heavy enough, it falls from the cloud. This takes 15 minutes to an hour.

According to Libbrecht’s calculations, enough snow forms in Earth’s atmosphere every 10 minutes to make a snowman for every living person on the planet. The vast majority, though, ends up melting before it ever hits the ground. But if the air is cold enough, snowflakes make it to the planet’s surface.

Libbrecht has traveled to places like Canada, Japan, and Sweden to study freshly fallen flakes firsthand. He catches them on a piece of foam as they drift down from the sky. Then he uses a paintbrush to carefully transfer the snowflakes to a glass slide. He quickly puts the slide under a microscope to examine each flake’s structure.

Snowflakes come in a wide variety of shapes. The most picturesque, says Libbrecht, are stellar dendrites, with their six branching arms. But snowflakes can also form prisms, needles, columns, and six-sided plates. By studying the size and shape of a snowflake, Libbrecht can determine the conditions under which it formed in the atmosphere (see Flake Formation). Temperature, for example, has the greatest effect on a snowflake’s shape. Humidity, or the amount of moisture in the air, affects how complex a snow crystal will be.

Libbrecht figured out how much snow forms in Earth’s atmosphere every 10 minutes. He says it’s enough to make a snowman for every living person on the planet. Most of it melts before it ever hits the ground. But if the air is cold enough, snowflakes make it to Earth’s surface.

Libbrecht has traveled to places like Canada, Japan, and Sweden. He goes to study freshly fallen flakes firsthand. He catches them on a piece of foam as they fall from the sky. Then he uses a paintbrush to carefully move the snowflakes to a glass slide. He quickly puts the slide under a microscope, and he looks at each flake’s structure.

Snowflakes come in many different shapes. Libbrecht says the prettiest are stellar dendrites. They have six branching arms. But snowflakes can also form prisms, needles, columns, and six-sided plates. Libbrecht studies the size and shape of a snowflake. That tells him the conditions in the atmosphere when it formed (see Flake Formation). For example, temperature affects a snowflake’s shape the most. Humidity is the amount of moisture in the air. It affects how complex a snow crystal will be.

In the lab, Libbrecht manipulates the same factors that affect snow crystal growth in nature to create his own flakes. He starts by quickly cooling a refrigerated chamber, causing moisture in the air to freeze into billions of glimmering ice crystals. They’ll become the seeds for new snowflakes.

Inside the chamber, some of the tiny crystals settle onto a chilled glass plate. By adjusting valves on the chamber, Libbrecht can control the temperature and humidity around the plate to coax the crystals to grow into an array of shapes. Using a microscope with a built-in camera, he can then view and photograph his creations.

Recently, Libbrecht wondered what would happen if he grew two snowflakes under the exact same conditions. He found two crystals right next to each other on his plate. Then he used the chamber to make sure they would experience the same changes in temperature and humidity. And voilà—he ended up with two look-alike snowflakes!

In nature, these “identical twin” snowflakes wouldn’t happen. It’s almost impossible for two crystals to encounter exactly the same conditions as they blow around separately inside a cloud. But Libbrecht is pleased to be able to make them in his lab. “It’s fun to figure out the recipe for growing the crystals,” he says.

In the lab, Libbrecht creates his own flakes. He uses the same factors that affect snow crystal growth in nature. He starts by quickly cooling a refrigerated chamber. This causes moisture in the air to freeze into billions of sparkling ice crystals. They’ll become the seeds for new snowflakes.

Inside the chamber, some of the tiny crystals settle onto a cold glass plate. Libbrecht adjusts valves on the chamber to control the temperature and humidity around the plate. That’s how he gets the crystals to grow into different shapes. Then he uses a microscope with a built-in camera. He can see and photograph his creations.

Not long ago, Libbrecht thought about a question. What would happen if he grew two snowflakes under the exact same conditions? He found two crystals right next to each other on his plate. Then he adjusted the chamber. He made sure they experienced the same changes in temperature and humidity. And he ended up with two look-alike snowflakes!

In nature, these “identical twin” snowflakes wouldn’t happen. Crystals blow around separately inside a cloud. So it’s almost impossible for two crystals to experience exactly the same conditions. But Libbrecht is pleased to be able to make them in his lab. “It’s fun to figure out the recipe for growing the crystals,” he says.

Libbrecht originally started studying snowflakes to get a better understanding of how other types of crystals form. Most solid materials have molecules arranged in a crystalline structure. Knowing how crystals are constructed can help scientists and engineers make everything from stronger cars to more-effective medicines.

The more Libbrecht studies snowflakes, though, the more he’s driven to make new shapes purely as art. His snowflake images have appeared in books, on posters, and in a series of postage stamps. He has also used his vast snowflake knowledge to advise other artists. Before Disney animators started working on the movie Frozen, they asked Libbrecht to show them how to draw snowflakes correctly.

Anyone can appreciate snowflakes, says Libbrecht—even if you don’t have a fancy lab. All that’s needed is a simple magnifying glass. Then the next time it snows, he says, “just go outside and have a look.”

At first, Libbrecht studied snowflakes for one reason. He wanted to better understand how crystals form. Most solid materials have molecules arranged in a crystalline structure. Scientists and engineers want to know how crystals are built. That can help them make everything from stronger cars to better medicines.

But Libbrecht has found another reason for studying snowflakes. More and more, he wants to make new shapes as art. His snowflake photos have appeared in books, on posters, and on postage stamps. Because he knows so much about snowflakes, he’s helped other artists. Disney animators called Libbrecht before they started working on the movie Frozen. They asked him to show them how to draw snowflakes correctly.

Anyone can enjoy snowflakes, says Libbrecht. And you don’t need a fancy lab to do it. All you need is a simple magnifying glass. Then the next time it snows, he says, “just go outside and have a look.”