Sampling organic molecules from a cometary nucleus

Abstract

The flybys of now four cometary nuclei revealed bodies with seemingly diverse topography and morphology. All cometary nuclei were active producing dust jets during the flybys but areas of activity could not be identified. Only the Deep Impact spectrometer observations revealed 3 small patches from which a signature of water ice crystals was discovered. These observations and the temperature maps demonstrate that the thermal inertia of the nucleus is very low. A corresponding low thermal conductivity was also inferred from the variation of the CO production of comet Hale Bopp with heliocentric distance. As a consequence a representative sample of the nucleus can easily be retrieved without drilling. This strongly facilitates a sample return from a cometary nucleus. Analyses of cometary material collected by Stardust with the aerogel collector and the CIDA instrument show that complex organic molecules are abundant. This instrumentation collected or analyzed, respectively, refractory material (dust grains) during the flyby through the inner coma of comet Wild 2. These grains had been lifted from the surface of the nucleus by gas drag of subliming ice. Therefore a probe directly picked from the (sub-) surface, sealed in a container, and returned to earth can be expected to comprise a representative sample of the nucleus material; certainly including complex organic compounds.