An explanation for the surprising number of triangular snowflakes seen in nature has been produced by two physicists at Caltech.

A paper published on the arXiv pre-print website by Kenneth Libbrecht and Hannah Arnold says aerodynmaics are behind the phenomenon.

While most snowflakes are hexagonal, triangular forms have long been observed. When Libbrecht and Arnold grew snow crystals in the lab they found far more triangular forms than would be expected from mere random growth perturbations.

Air moving past a falling crystal will increase its growth, they note. A tiny factor – perhaps a piece of dust on the crystal – that causes a small change in growth of a perfect hexagon will also tilt the crystal, changing the way air moves past the crystal and – in their model – increasing the way the crystal grows at certain points and inducing a more triangular appearance.

“The end result is that an initial symmetry-breaking perturbation results in a growth morphology that becomes more triangular with time,” the paper says. “Only one initial perturbation is necessary, and no coordination intrinsic to the molecular structure of the crystal need be present.”

[Hat tip: Science News.]

Images: Ken Libbrecht