Phase Trapping in Acetonitrile, a Metastable Mineral for Saturn's Moon Titan

Acetonitrile has been observed within the atmosphere of Titan, Saturn's largest moon, and as a result, it is assumed that it will be a significant surface solid (mineral) upon Titan. Solid acetonitrile is known to adopt high-temperature (alpha) and low-temperature forms (beta), with the beta form assumed to be the stable phase under Titan's surface conditions. We present experimental evidence (powder X-ray diffraction and differential scanning calorimetry) that on rapid cooling, the high-temperature alpha form can persist at low temperature, making it a viable mineral species for Titan, analogous to cristobalite (the quenched high-temperature form of silica) on Earth.