Composition of comet Halley dust particles from Giotto observations

Mass spectra of cometary dust particles measured by the PIA dust particle analyser aboard the Giotto spacecraft show some unexpected and striking features. First, small particles below 10^-14 g are much more abundant than anticipated by models. Second, most of the particles are rich in light elements such as H, C, N and O, suggesting the validity of models that describe the cometary dust as including organic material. Third, the light elements specifically seem to have a low ratio of mass to volume. Three examples of original mass spectra showing typical compositions are given; these have been measured and are compared with a computer-simulated mass spectrum.