Ch. 16-5 Small Bodies in the Solar System Pages 500 - 505

COMETS Ion tail - electrically charged particles from solar wind. *A comet is a small body of ice, rock, and cosmic dust loosely packed together. “Dirty Snowballs” Ion tail - electrically charged particles from solar wind. Nucleus -the solid center. Dust tail - gas and dust when ice melts from the sun’s heat.

Comet Shoemaker Levy July 1994 Impact with Jupiter

Where Do Comets Come From? *Many scientists think they come from a spherical region called the Oort cloud that surrounds the solar system. The gravity of a passing planet or star disturbs part of this cloud and comets are pulled in toward the sun.

ASTEROIDS *Asteroids are small, rocky bodies in orbit around the sun. They can be a few meters to nearly 1000 km in diameter.

Where do Asteroids Come From? * From the asteroid belt which is a wide region between the orbits of Mars and Jupiter.

METEOROIDS * If a meteoroid enters the earth’s atmosphere and strikes the ground it is called a meteorite. * A meteoroid is a small (much smaller than asteroids), rocky body orbiting the sun..

SHOOTING STARS (are not stars at all!) *The bright streak of light caused by a meteoroid or comet dust burning up in the atmosphere is called a meteor.

Composition of Meteorites Stony meteorites are similar to the composition of rocks you would find on Earth. Metallic meteorites are made of mostly metals. Stony-metallic meteorites, the third type, contain iron and stone.

Why does the moon have so many impact craters? *The Earth has an atmosphere which acts like a shield in which small bodies burn up before they reach the surface. *The moon has no atmosphere to protect it. Also, there is no weathering on the moon to erase the craters.

Impacts on Earth Most objects that come close to Earth are small and usually burn up in the atmosphere. About 65 million years ago, a meteor 10 km wide struck Earth and caused 15-20% of all species, including the dinosaurs, to become extinct. Meteor Crater Arizona Most craters on the Earth are hidden by erosion, plants or the oceans.