THE COMET EXPERIMENT

The COMET program is a program for the collection of micron to submicr on interplanetary dust particles in low Earth orbits. Since collection takes place as the Earth crosses a given meteor stream, the particles are mainly of cometary origin. The grain remnants, located at their i mpact positions on high purity metallic collectors, are analysed in th e laboratory for chemical and isotopical identification. The COMET-1 e xperiment took place in 1985 October, during encounter with the Dracon id meteor stream, related to the Giacobini-Zinner comet. The fluence o f extraterrestrial grains that had impacted our detectors was approxim ately 10x higher than the value of the mean meteroid fluence at approx imately 1AU, which suggests that most of the grains originated from th e Giacobini-Zinner comet. One of the most important results of their c hemical analysis was that approximately 90% of them are enriched in lo w Z elements (C and O have undoubedly been identified). They could con tain a CHON phase similar to that observed in the close environment of Halley's nucleus. The first imagery of the grain remnants by field em ission scanning electron microscopy suggests that they are very law de nsity aggregates still present at the impacting positions which, in mo st cases, are very different from the impact craters observed for the same mean relative velocity for full grains of the same size. These re sults show that the COMET program has constituted an important step to wards the analysis of cometary material and the understanding of the e volution of the early Solar System.