Comets, Asteroids, Meteoroid and Meteorites Chapter 21 Section 5 Pages 668-673

Comets A comet is a small body of ice, rock and cosmic dust loosely packed together. Scientists refer to them as dirty snowballs.

Comet’s Orbit Comets orbit the Sun in highly elliptical orbits. Their velocity increases greatly when they are near the Sun and slows down at the far reaches of the orbit. Since the comet is light only when it is near the Sun (and is it vaporizing), comets are dark (virtually invisible) throughout most of their orbit. The solar wind pushes the tail away from the Sun.

Parts of a Comet When they are near the Sun and active, comets have several distinct parts: Nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids; Coma: dense cloud of water, carbon dioxide and other neutral gases Hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen; Dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye; Ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind.

The comet's tail gets bigger as it gets closer to the sun and then decreases as it moves away from the sun.

Comets Facts A comets ion tail always points away from the sun. Solar winds blow the ion tail away from the sun. The dust tail follows the comet’s orbit and does not always point away from the sun. Scientists believe that comets come from the Oort Cloud, a region that surrounds the solar system. Comets can also come from the Kuiper Belt which exists outside of Neptune’s orbit.

Shoemaker-Levy Comet On 1994 July 16-22, over twenty fragments of comet Shoemaker-Levy 9 collided with the planet Jupiter. The comet, discovered the previous year by astronomers Carolyn and Eugene Shoemaker and David Levy, was observed by astronomers at hundreds of observatories around the world as it crashed into Jupiter's southern hemisphere.

Video Link to NEO’s (Near Earth Objects) http://neo.jpl.nasa.gov/neo/

Asteroids Asteroids are small rocky bodies that revolve around the sun. They range in size from a few meters to more than 900 kilometers in diameter. Asteroids have irregular shapes, but some are spherical, or round. Most asteroids orbit the sun in asteroid belt. The asteroid belt orbits between Mars and Jupiter. Asteroids are thought to be left over from the formation of the solar system.

Meteoroids, Meteors and Meteorites Meteoroids are small rocky bodies that travel through space. A meteor is a bright streak that results from a meteoroid burns up in Earth’s atmosphere, what we call shooting stars. A meteorite is a meteoroid that reaches the Earth’s surface without burning up.

Three Types of Meteorites Stony- Rocky material Metallic- Iron and Nickel Stony Metallic- Rocky material, iron and nickel

Stony Meteorites Rocky material

Metallic Meteorite iron and nickel

Stony-Iron Meteorite rocky material, iron and nickel

Meteorite Crater-Winslow, Arizona This crater was formed approximately 50,000 years ago when an iron mass, estimated to be about 80 feet in diameter and weighing over 60,000 tons entered the Earth's atmosphere over the American Southwest. The resulting formation is about 4,000 feet (1,200 meters) wide and 570 feet (175 meters) deep.

A fragment of the meteorite that created Meteorite Crater. Metallic Meteorite