The smallest long lived nanoparticles in the atmosphere (radius<2 nm) condense from evaporated meteoric material in the mesopause region (h~85 km). There they give rise to an abnormally high radar reflectivity and during summertime at high latitudes act as nuclei for the spectacular noctilucent clouds. We investigate the chemical and physical processes leading to the formation and growth of these ice clouds in the laboratory. To do so, we have developed a unique simulation chamber to expose nanoparticles to the extreme conditions of the mesopause.