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.