Single minerals, carbon- and ice-coated single minerals for calibration of GIADA onboard ROSETTA to comet 67P/Churyumov–Gerasimenko

• We present our rationale for cometary dust analogs selection.
• We report chemical and morphological characterization of cometary analogs.
• Analogs: monomineralic grains as such and coated by amorphous C or Na2SiF6.
• Minerals: Mg, Fe and Ca–K–Na silicates, phyllosilicates, pyrrhotite, and corundum.
• Cometary analogs are used to calibrate GIADA/Rosetta performances.

In preparation of the rendezvous of the European Space Agency Rosetta spacecraft with short period Jupiter Family comet 67P/Churyumov–Gerasimenko we undertook the selection and characterization of mineral grains to serve as analogs of dust from the comet. Specifically, these dust analogs are used to calibrate the performance of the onboard Grain Impact Analyser and Dust Accumulator (GIADA) instrument at the comet. Our selection of suitable natural analog minerals was guided by the finding of an asteroid-like mineralogy in Jupiter Family comet Wild 2. We selected (1) anhydrous silicate minerals [forsterite and fayalite (end-members of the olivine solid solution series), enstatite, melilite, alkali-feldspar and anorthite], (2) hydrated layer silicates (kaolinite, serpentine, and talc), (3) pyrrhotite, and (4) corundum. Four size fractions, viz. 500–250 µm, 250–100 µm, 100–50 µm and 50–20 µm, were prepared for each analog mineral. In addition, each selected analog mineral, from each size bin, was coated with carbon layer. Similarly another set of analog grains were coated with a layer of sodium hexafluorosilicate (Na2SiF6) crystals representing comet water-ice, for what concerns their optical properties. Laboratory experiments to calibrate the GIADA performance using these analogs are currently underway. We report the availability of analogs that will enable the calibration of various instruments onboard Rosetta.