Comet Dust

Because the particles are so small, their surfaces can only be studied in detail using electron microscopy. This scanning electron microscope photograph shows a grain about 10 microns (.0004 in) wide, which has a very open structure, presumably once filled by icy comet material. As these particles are ejected from comets, the ice immediately sublimes (turns from solid to gas), leaving a framework of dust similar in comparison to ancient carbon-rich meteorites.