The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on the SciSat satellite measured nearly 30 spectra of polar mesospheric clouds (PMCs) between 65¿ and 70¿N from July 5 to 14, 2004. The ACE-FTS measurements are augmented by UV observations made at the same latitude and time period by the Optical Spectrograph and Infrared Imager System (OSIRIS) on the Odin satellite. Our analysis of these measurements shows that PMC particles are composed of nonspherical ice crystals with mean (equivalent spherical) particle radii of 59 ¿ 5 nm.