SNOWFALL in Pasadena, California, is so rare, it’s almost unheard of. Except, that is, at the California Institute of Technology, where Kenneth Libbrecht can conjure it up using the world’s most sophisticated snowflake-making equipment.

As a physicist, Libbrecht has tackled some fairly epic questions, like the nature of gravitational waves and the internal workings of the sun. But he also has a delightful sideline in the , which are far more . One of the biggest unanswered questions about them is why they appear to come in two distinct types.

Libbrecht went on a 20-year odyssey to solve this mystery. Recently, he published the fruits of that journey in the form of . It contains a kind of grand unified theory of snowflakes, explaining for the first time how and why they grow into the delicate shapes they do.

Joshua Howgego: What got you interested in snowflakes?

Kenneth Libbrecht: One day I was chewing the fat with one of my students and we got talking about how crystals grow and take on shapes. We started thinking about what we could study in this area and I thought: well, water would be cheap and easy. Then I thought: actually, that would be the physics of snowflakes, I wonder how that works? Apropos of nothing – I was just curious – I started reading up on research on snowflakes and I found it really fascinating.

What was the big question about snowflakes?

The standard snowflakes you see in holiday decorations – six-pointed, thin and flat – well, that’s not the way they always form. As well as thin, hexagonal plates, they can grow into tall, hexagonal columns, like the shape of a pencil in miniature. It was discovered in Japan in the 1930s that these two forms of snowflake will form at different temperatures. Plates will form at around -2°C, columns at about -5°C and then plates again at about -15°C. It’s such a crazy pattern that it flops back and forth like that. I really wanted to know why it happens, but it turned out there was no answer – it was a complete mystery.

How did you investigate this conundrum?

I decided the way to answer this question was to systematically grow a lot of snowflakes in different conditions and measure their growth. This was 20 years ago, and for several years I kept hitting problems and made no progress. I eventually figured out the whole experiment has to be enclosed in a box. You add in water vapour, but the conditions, like temperature and pressure, have to be precisely controlled. I have all these little rods going into the box that I use to push things around and turn things on and off. Then I could grow crystals – mostly I grew ones that are smaller than the width of a human hair and then studied them under a microscope. If they get too large, they are too complicated in shape to study easily.

You recently published what has been called a grand unified theory of snowflakes.

People had always thought that if you have a flat surface in a crystal, it always grows in the same way under given conditions. What I found is that in snowflakes, the size of the surface matters quite a lot. If you imagine a hexagonal, plate-like snowflake, it has two wide surfaces and then six much thinner surfaces around the edge. It turns out that those thinner surfaces grow much faster than the broader surfaces, and this creates a runaway effect where you get thinner and thinner plates. The fun thing is that this trend reverses – at certain temperatures, it’s the wider surfaces that grow faster, and so you get column-like crystals.

To understand this fully, you need to dig down into the details about the molecular structure of the ice crystal surface and how it changes with temperature on different surfaces. So far, my model seems to fit all the data, so it is encouraging that at least some of the mystery has been solved.

Does your work tell us anything about what snow would be like on other worlds, such as Saturn’s icy moon Enceladus?

The diffusion of water molecules through the air affects snowflakes’ growth in a way that reinforces the molecular effects to create the thin edges seen in plate-like and hollow-column crystals. When I grow crystals in a vacuum, none of this happens. So, yeah, there would be differences in snow on other planets. If there’s no atmosphere, you are going to get blocky crystals, but at high pressure you would get incredibly thin ones. Of course, the chemistry of the atmosphere could change this, too, in ways that are hard to predict.

You have also grown two identical snowflakes. I thought that was supposed to be impossible.

This started when, early on in my snowflake work, I realised there were no good videos of snowflakes growing. I wanted to make one showing a perfect-looking crystal. Eventually, I worked out how to grow crystals on a fixed support and film them. They looked so much better than crystals that fall from the sky. They were crisper, sharper. Real snowflakes have had kind of a hard life, falling through the atmosphere and banging into other flakes. They have also begun to evaporate, so the edges are always a little rounded.

In the lab, though, I can turn knobs to control the conditions exactly – I can even change things slightly to make the growing crystals branch – and so I can get these designer snowflakes. Then I realised that if you grow two snowflakes next to each other in the box and grow them at the same time, under the same conditions, they come out very similar. Everybody seems to have heard this old adage that no two snowflakes are alike, but then this crazy person is making snowflakes that are alike.

What kinds of questions are still unanswered when it comes to snowflakes?

My model is very complicated. But it makes a lot of predictions and I want to test those out, see what happens and hopefully refine the model. One of the predictions is that interesting things might happen to snowflakes close to their melting point. You might see what’s called pre-melting, where most of the snowflake is a rigid crystal, but on the surface the molecules get disordered. I’ve been trying to explore that. I’m also trying to make larger crystals; I’d like to make the world’s largest snowflake. For no particular reason… there’s just always something new to try.

When you go out in the snow these days, do you see it in a new light?

I grew up in North Dakota, where it gets very cold and we have a lot of snow. I used to see six-pointed star flakes, large ones, but I didn’t know any of this stuff. Now I know a lot better what to look for. I’ll go out and have a magnifier and be looking for different kinds of flakes – like capped columns, for instance, which are like a special hybrid of the plate and column types. I call it snowflake watching. The funny thing is, my wife is a botanist, and when we go out together she’s always looking at the different plants – but they all look like weeds to me.

“Children are, in fact, quite sophisticated in deciding who and what they trust”

Check your conspiracy

AS ANY young child knows, reindeer have a special superpower: they can fly. Or, at least, Rudolph and his eight sleigh-towing pals can. Reindeer first took to the skies in 1823, when Clement Clarke Moore published Twas the Night Before Christmas. He is said to have got his inspiration from the Sami people of northern Europe, whose shamans conjured up flying reindeer while in magic mushroom-induced trances.

Read more: Find all our holiday long reads here

Unfortunately, that’s all bunkum – even the bit about the Sami. But who needs fiction? Reindeer have real-world superpowers. The animals have evolved a whole range of amazing innovations that let them not just survive but thrive in the frigid Arctic. Their , from gold in summer to blue in winter. They see the world in glorious ultraviolet. They can switch their body clocks on and off, produce lots of vitamin D even in limited sunlight and grow antlers up to a metre long in just a few months.

What’s more, we might be able to borrow some of those abilities. Discovering more about Rudolph could lead to new ways of tackling jet lag, insomnia and cancer, and even allow us to grow new limbs. Thanks to recent work revealing the genetic underpinnings of reindeer’s unusual traits, their superpowers could one day be ours.

Nearly 5 million reindeer roam the frozen north, from Alaska to Siberia and Greenland. The biggest group, containing about half a million animals, is the Taimyr herd of the Siberian tundra. Also known as caribou in North America, these lichen-eating ruminants are the by humans and about half are domesticated. On the Norwegian islands of Svalbard, males of the smallest subspecies weigh no more than 90 kilograms. In the forests of Finland, a stag can tip the scales at 250 kilograms.

Wherever they live, reindeer face challenges that would kill many other animals, including severe cold, limited food in winter and extremely prolonged periods of daylight and darkness. In June this year, some of the genes that allow them to overcome these problems were revealed in the first results from the . It compared reindeer DNA with that of other animals that chew the cud and identified mutations galore. “We were surprised to find so many unique gene variants related to reindeer’s adaptation to the Arctic environment,” says Zhipeng Li at the Chinese Academy of Agricultural Sciences.

“Many of the same genes are involved in the same processes in reindeer as they are in humans,” says Rasmus Heller at the University of Copenhagen, Denmark, who was also part of the project. Take the biological clock. Humans and most other animals have daily rhythms of activity and inactivity linked to light and dark, driven by the circadian clock. Reindeer do too, but they can override this. In the 24-hour daylight of an Arctic summer, they forage almost around the clock so they can put on as much weight as possible. In the dark depths of winter, their metabolic levels plummet and they have only short bouts of activity that don’t adhere to a 24-hour pattern.

They share this ability to break the rhythm of the circadian clock with other polar animals, including the emperor penguin and a type of grouse called the rock ptarmigan. “If you are an Arctic animal, you are faced with the weirdness of the light conditions,” says Heller. “This is a challenge for an animal that doesn’t have the genetic background to cope with it. It would mess with everything from hormone secretions to physiology.” The ruminant genome studies reveal what is going on in reindeer. They have unique versions of genes that drive circadian rhythms. In particular, this means one key protein called Per2 is mutated, so that another protein crucial for this regular cycle can’t bind to it. “A vital part of their biological clock malfunctions,” says Heller.

A cure for jet lag?

The discovery of these gene variants in reindeer could perhaps be exploited to help humans overcome jet lag, which results from having to readjust to the light/dark cycle in a different time zone. Disruptions to circadian rhythm are also thought to play a role in mood disorders such as depression.

The biological mechanisms underpinning how reindeer override their circadian rhythms could provide insight into sleeplessness, too. “There are specific gene variants involved in insomnia, and we can compare these with the genes from reindeer to further understand how people’s circadian rhythm is affected,” says Li.

Another impressive ability is the way both male and female reindeer grow new antlers every year. Aside from the placenta, deer antlers are the only mammalian organs that can be completely regenerated. A reindeer’s headgear can contain up to 10 kilograms of bone and blood vessels, and grows up to 2.5 centimetres a day. How do they achieve this?

provides an answer. “The genes that get turned on in cells destined to become antlers are also turned on in cancer cells” says Yunzhi Peter Yang, a tissue engineer at Stanford University in California. “Tissue regeneration and cancer growth are two sides of the same coin.” Yet reindeer are five times less likely to get cancer than other mammals because they have evolved highly efficient tumour suppression mechanisms that control the otherwise dangerous cancer pathways. This extraordinary ability makes them of great interest to researchers looking for new ways to prevent or treat cancer in humans.

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Growing antlers also requires a lot of calcium, and that presents another challenge. To absorb calcium from food in the gut, mammals need vitamin D, which is made through the action of sunlight on skin. “It is particularly important for reindeer to maximise their calcium uptake and vitamin D production, but this is challenging in an environment where there is essentially no sunlight for half the year,” says Heller. The reindeer’s solution, , is a souped-up system for producing vitamin D that is far more efficient than ours.

Understanding how reindeer antlers grow might help us regenerate tissues in humans. “Can we borrow the same mechanisms for bone diseases such as osteoporosis or bone cancer?” says Yang. “There is so much potential.”

Some of it has already been realised: the way antlers are attached to the skull has inspired the design of a for people missing limbs.

Flying and red noses are all very impressive but it turns out that the real reindeer powers are just as exciting – and, more importantly, they’re not just for Christmas.

Bantha milk (Star Wars: A New Hope)

´Ąłž˛ú°ů´Ç˛őžą˛šĚý(Battlestar Galactica)

Pan galactic gargle blaster (The Hitchhiker’s Guide to the Galaxy)

Gethen beer (The Left Hand of Darkness)

Watch

Film Festival, at Regent’s Place from 17 July, is full of stories of how we can all treat the planet a little more kindly. There is also the promise of “indulgent vegan dirty jackfruit”. Exciting times…

Visit

Festival, from 20 to 21 July, offers visitors the latest botanical science in the beautiful and biodiverse setting of the Royal Botanic Gardens, Kew, in London. This year’s theme is “rare and threatened”.

Read

in the Heavens: How infrared astronomy is expanding our view of the universe by Michael Werner and Peter Eisenhardt (Princeton University Press) tours the cosmos through the Spitzer Space Telescope.