ASTEROIDS, COMETS, AND METEOROIDS

ASTEROIDS, COMETS, AND METEOROIDS 

ASTEROIDS, COMETS, AND METEOROIDS  are all debris remaining from the nebula in which the solar system formed 4.6 billion years ago. Asteroids are rocky bodies up to about 1,000 km in diameter, although most are smaller. Most  of them orbit the sun in the asteroid belt, which lies between the orbits of mars and Jupiter. Comets may originate in a huge cloud (called the Oort cloud) that is thought to surround the solar system. They are made of frozen gases and dust, and are a few km in diameter. Occasionally, a comet is deflected from the Oort cloud to the orbit the sun in a long, elliptical path. As the comet approaches the sun, the comet's surface starts to vaporize  in the heat, producing  a  brightly shining coma (a huge sphere of gas and dust around the nucleus ), a gas tail, and a dust tail. Meteoroids are small chunks of stone or stone and iron, some of which  are fragments of asteroids  or comets. Meteoroids range in size from tiny dust particles to objects tens of meters across. If a meteoroid enters the Earth's atmosphere, it is heated by friction and appears as glowing streak of light called a meteor ( also known as a shooting star). Meteor showers occur when the Earth passes through the trail  of dust particles left by a comet. Most meteors burn up in the atmosphere. The few that are large enough to reach the Earth's surface are termed meteorites.