Small Bodies: Asteroids and Meteoroids

The largest grains of interplanetary dust, or micrometeoroids, continually intersect the Earth. They are still so lightweight that, once in the atmosphere, they float gently down to the ground. In addition to these barely discernable pellets, other small rocky and metallic bodies called the meteoroids routinely strike the Earth. Meteoroids have random orbits about the Solar System. Meteoroids cause the smaller craters that appear abundant on planetary surfaces with little or no atmosphere. Moving at supersonic speeds, meteoroids explode upon impact, excavating a crater. Creating a large basin requires an asteroid or large comet. Occasional, large meteoroids create bright meteors called the bolides. A meteor may cause damage without reaching the Earth&s;s surface or creating a crater. One of the great natural mysteries of modern times is the Tunguska Event, so named because scientists do not quite know what happened in central Siberia in 1908.