| interplanetary dust |
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Micrometeoroids present in the space between the planets. The particles are thought to originate in collisions between asteroids in the asteroid belt and from the gradual break-up of comets. Fragments from comets initially form meteor streams, but will disperse over long periods of time. The zodiacal dust cloud extends out from the centre of the solar system for at least 600 million kilometres (373 million miles). Its presence is observed as the zodiacal light: sunlight scattered by dust particles a few tens of micrometres in size. Its very low density is equivalent to one grain in a cube hundreds of metres across at the Earth's distance from the Sun. Near the Sun, the particles are eroded by collisions, evaporation and the action of the solar wind. The Infrared Astronomical Satellite (IRAS) located three dust bands between Mars and Jupiter in the asteroid belt. The brightest is centred on the ecliptic, but there are fainter bands 10° to the north and south of the ecliptic. These are thought to consist of dust particles in orbits tilted at about 10° to the ecliptic. See also: Poynting-Robertson effect. |