Meteors, Comets, Asteroids Meteoroid – a relatively small chunk of rock or metal orbiting the sun. Meteoroids are called meteors when they enter earth’s atmosphere. Most are so small that they burn up and glow when they enter the atmosphere because of friction between the meteor and the atmosphere (referred to as shooting stars). When earth crosses the orbit of a stream of meteoroids, the result is a meteor shower. These showers occur at regular times throughout the year. Meteorites are meteors that do not completely burn up when entering earth’s atmosphere, and instead, land on earth. Asteroid – chunk of rock or metal orbiting the sun (larger than meteoroids) Most are in orbit between Mars and Jupitor in the asteroid belt. Can have a diameter of up to 940 km. In 2000, the NEAR (Near Earth asteroid Rendevous) went into orbit around the asteroid EROS, and also was the first spacecraft to soft land on an asteroid. Comet – an object composed of dust and rock particles, ice, methane, and ammonia that orbits the sun in an elliptical path. The nucleus is the solid part of the comet. As a comet approaches the sun, the ice and gases vaporize, releasing dust and rock particles, forming a coma, or bright cloud, around the nucleus. The solar wind pushes on the gases and dust, forming tails that point away from the sun. Short Period Comet – has an orbital period of less than 200 years. Ex: Halley, Comet Encke Long Period Comet – orbital period of more than 200 years. Ex: Hale-Bopp, Hayakutake Comet Encke Oort Cloud – is a cloud of comets located beyond the orbit of Pluto. .