Is every snowflake different?

Answers to your questions about the news.
July 20 2006 6:42 PM

Are Snowflakes Really Different?

Some ice crystals look exactly the same.

Download the MP3 audio version of this story here, or sign up for The Explainer's free daily podcast on iTunes.

President Bush exercised the first veto of his presidency on Wednesday, turning down a bill that would have increased the scope of human embryonic stem-cell research. Several dozen "Snowflake" babies—born from frozen embryos that had been donated rather than destroyed—were on hand to help celebrate the announcement. The Snowflake Embryo Adoption Program took its name "because embryos are unique and fragile." Is each snowflake that falls from the sky really unique?

Yep, although it may not always look that way. As snowflake expert Kenneth Libbrecht has pointed out, any two ice crystals of a reasonable size are going to be different on the atomic level. That's because ice crystals are made up of water molecules, which aren't always exactly the same. Some water molecules have an atom of deuterium in place of one of the hydrogens, and others have an atom of O18 in place of the regular O16. Even a smallish crystal might comprise a quintillion water molecules—so the chance that any two would have the same pattern of deuterium and O18 atoms is effectively zero.

Advertisement

On the gross level, though, snowflakes can look very much alike. In 1951, the International Commission on Snow and Ice divided ice crystals into seven basic shapes, ranging from "stellar crystals" to "irregular forms." More recent schemes have subdivided those categories into 35, 41, or even 80 distinct types. The simplest among these is the hexagonal prism—which serves as the foundation for all of the more complex crystal forms. A pair of these basic shapes could look identical under the microscope. (Like ice crystals, not all "Snowflake" children appear unique to the naked eye. Among the 110 babies who have been born through the program are two sets of identical twins.)

Most ice crystals that fall from the sky are "irregular," which means they can have any shape at all. To say that no two irregular snowflakes are alike is akin to saying that no two grains of sand are alike, or no two specks of dust. It's more interesting to point out that the more intricate, symmetrical snowflake forms (like the stellar crystals) never repeat themselves. That's because a complex snowflake grows in different ways depending on the weather conditions it experiences in the sky. A single ice crystal might get blown from one temperature and humidity zone into another many times before it falls to the ground. The exact timing of these movements determines its eventual shape. (For example, a flake that starts growing as a cylinder might end up in conditions that are more conducive to the growth of disklike crystals. The end result would be a "capped column," or something that looks a bit like a Star Wars tie fighter.)

Got a question about today's news? Ask the Explainer.

Explainer thanks Kenneth Libbrecht of the California Institute of Technology and Ron Stoddart of the Snowflake Embryo Adoption Program.

Daniel Engber is a columnist for Slate

TODAY IN SLATE

Politics

Blacks Don’t Have a Corporal Punishment Problem

Americans do. But when blacks exhibit the same behaviors as others, it becomes part of a greater black pathology. 

I Bought the Huge iPhone. I’m Already Thinking of Returning It.

Scotland Is Just the Beginning. Expect More Political Earthquakes in Europe.

Lifetime Didn’t Think the Steubenville Rape Case Was Dramatic Enough

So they added a little self-immolation.

Two Damn Good, Very Different Movies About Soldiers Returning From War

Medical Examiner

The Most Terrifying Thing About Ebola 

The disease threatens humanity by preying on humanity.

Students Aren’t Going to College Football Games as Much Anymore, and Schools Are Getting Worried

The Good Wife Is Cynical, Thrilling, and Grown-Up. It’s Also TV’s Best Drama.

  News & Politics
Weigel
Sept. 20 2014 11:13 AM -30-
  Business
Business Insider
Sept. 20 2014 6:30 AM The Man Making Bill Gates Richer
  Life
Quora
Sept. 20 2014 7:27 AM How Do Plants Grow Aboard the International Space Station?
  Double X
The XX Factor
Sept. 19 2014 4:58 PM Steubenville Gets the Lifetime Treatment (And a Cheerleader Erupts Into Flames)
  Slate Plus
Slate Picks
Sept. 19 2014 12:00 PM What Happened at Slate This Week? The Slatest editor tells us to read well-informed skepticism, media criticism, and more.
  Arts
Brow Beat
Sept. 19 2014 4:48 PM You Should Be Listening to Sbtrkt
  Technology
Future Tense
Sept. 19 2014 6:31 PM The One Big Problem With the Enormous New iPhone
  Health & Science
Bad Astronomy
Sept. 20 2014 7:00 AM The Shaggy Sun
  Sports
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.