Water’s complicated phase diagram may need to be updated. Kyung Hwan Kim of Stockholm University and colleagues used femtosecond X-ray laser pulses to probe micrometre-sized water droplets supercooled in a vacuum. Measuring the diameter of the drops as they evaporate and cool, the team found evidence for a supercooled liquid phase at 229 K for water and 233 K for heavy water (consistent with a “Widom line” separating the two liquid phases). Remarkably, water can remain liquid down to –42.55 °C.

Further reading
K Kim et al. 2017 Science 358 1589.