New link between Earth and asteroids.

Astronomers have found indirect evidence that Earth is embedded in a ring of asteroidal dust particles that orbits the sun. According to Stanley Dermott and Sumita Jayaraman of the University of Florida in Gainesville and their colleagues, the ring may funnel asteroidal dust -- which includes carbonaceous material that may help foster life -- into Earth's atmosphere.

This intriguing conclusion stems from the overlap of two studies -- an investigation of the dynamics of interplanetary dust particles an observations taken in 1983 with NASA's Infrared Astronomical Satellite (IRAS), notes Dermott.

Researchers have long known that asteroids collide, creating micrometer-size dust particles. The influence of solar radiation causes the particles to leave the asteroid belt, which lies between Jupiter and Mars, and spiral toward the sun. But on their way their encounter the terrestrial planets -- Mars, Earth, Venus, and Mercury. Dust particles may become temporarily trapped in ring-shaped solar orbits, some of which brush past these planets.

Jayaraman and Dermott calculate that about 20 percent of asteroidal dust particles 12 micrometers or more in diameter form such a ring near Earth. Each particle remains trapped in the ring for some 10,000 years, but the ring is constantly replenished by new arrivals. Earth sits in a tiny cavity in the ring.

Their simulation indicates that the portion of the ring trailing Earth is denser and closer to the planet than the part in front. This model, says Dermott, matches exactly IRAS observations that a brighter could of dust trails Earth than leads it at all times of the year. The researchers speculate that this dust ring near Earth creates a bottleneck, impeding the passage of particles on their way to the sun and increasing the likelihood that Earth's gravity will pull these bits of asteroids into our atmosphere.