Clathrate Snowflake -- Image credit: Timothy Strobel, Carnegie Institution for Science, Geophysical Laboratory

This image was selected as our holiday card for 2012. The snowflake is based on a new structure of “filled” ice discovered recently at the Geophysical Laboratory. Hydrogen-bonded water molecules (red) form a network of channels that trap hydrogen molecules (green) inside. This structure forms when mixtures of water and hydrogen are compressed above 5000 atmospheres at moderately cool temperatures (below 10 °C).