Cosmic Dust Grain
A speck from a comet?
Displayed in a close-up under an electron microscope, this tiny bit of cosmic dust may be our first sample of a passing comet. Less than one-tenth of a millimeter across, the particle is composed of millions of even tinier crystals. Although chemically similar to some meteorites, its fluffy, crystalline structure is unlike that of any known meteorite. Interplanetary dust particles like this are trapped in special collectors flown aboard high-altitude aircraft. Their interplanetary origin is established by analyzing the gases that they trapped from the Sun while still in space. The interplanetary dust is believed to come from comets, which shed material as they are warmed by the Sun. It may be possible to collect material from a particular comet when one passes close enough to the Earth some day.
Photograph and caption, NASA.