Stardust.

Rocket experiments were conducted to collect particles from noctilucent clouds at Kiruna, Sweden. The Pandora II inflight shadowing technique considered by Hallgren and Hemenway (1971) was used in the experiments. This technique makes it possible to study the collected particles as a function of time and altitude intervals. The particles observed consisted of an irregular electron-opaque core surrounded by a rounded, low density material. X-ray and electron opacity data suggest that the abundances of the heavy elements, such as Hf and Ta, in the particles are comparable to those of the light elements, such as Al and Si.