How an Ice Star is Born from Watery Chaos ✛ ✎ ✦
Rapid freezing sets off an unusual scenario in water. First, the tiniest cubic seeds are born — like seeds that dictate the future shape. Just as the first grain in an ear of corn sets the direction of growth, so these centers force the ice to branch at an angle of 109.5 degrees. The result is an eight-rayed ice star, an octahedron.
Scientists cooled a droplet to −40 °C and, using machine learning, analyzed millions of images to distinguish cubic ice. Simulations confirmed that cubic seeds are the chief architects of growth. Similar processes occur in carbon during the birth of diamonds and in silicon for microchips. Understanding such crystallization will improve materials technology and tissue freezing.
Thus, the microscopic chaos of molecules in an instant turns into mathematically precise symmetry — a subject pondered by Kepler, Faraday, and Boltzmann.
Cubic ice is sometimes found in the highest and coldest clouds of Earth's atmosphere. Its microscopic crystals are so symmetrical that they resemble tiny diamond octahedrons.
Kurt Vonnegut's novel Cat's Cradle describes ice-nine, a substance that instantly freezes water. The discovery of cubic seeds echoes this plot: a single tiny crystal can trigger an avalanche of crystallization, albeit without apocalyptic consequences.