Comets, Asteroids and Meteors

Comets

• Chunks of ice and dust that orbit the sun in very long narrow ellipses.
• Can be thought of as a "dirty snowball"

• Approaching the Sun
• As they approach the sun, energy from the sun "melts" the ice that holds the dust together.
• The dust makes a debris trail that stays in orbit
• When it is going away from the sun it will eventually be far enough away that it freezes and stops releasing gas and dust

• Structure
• Gas and dust form an outer layer called the coma
• Ice and dust held together by the ice makes an inner layer called the nucleus
• The brightest part, called the Head, is made up of the Coma and the Nucleus
• As gasses are released from the head the solar wind pushes them away from the sun forming a long "tail"

• The tail ALWAYS points AWAY from the sun no matter where it is in its orbit (approaching the sun or going away from the sun)

• The Oort Cloud
• In a region of space about twice as far from the sun as Pluto at the ver edge of the sun's influence
• Thought to be left-overs from the formation of the solar system
• The "home" of comets

• Halley's Comet
• 1705 Edmund Halley studied reports of comet sightings over hundreds of years, he realized that several reports occurred at regular intervals 76 years apart
• He predicted that it would return in 1758, it did and was named after him!
• The last time Halley's comet appeared was 1986 it was visited by the European Space Agency spacecraft Giotto

Asteroids

• 1801-1807 four small rocklike objects were discovered orbiting between Mars and Jupiter
• over the next 80 years 300 more were found, now we know of 10,000's
• Too small to be called "planets" they were called asteroids
• Most orbit between Mars and Jupiter in a region called the Asteroid Belt
• Some asteroids are knocked out of the asteroid belt and are in "Near Earth" orbits. The Earth has been hit by asteroids in the past.
• 65 million years ago one hit and made a crater 200Km across near the Yucatan Peninsula near Mexico, some think this lead to the extinction of the dinosaurs.

Meteors

• Meteoroids - a chunk of rock or dust in space, usually come from comets or asteroids.
• When a comet gets near the sun in its orbit, it begins to "melt" and release dust and rock creating a debris trail. This rock and dust in the debris trail can be classified as meteoroids.

• Meteors- a bright streak of light in the sky created when a piece of rock or dust in space enters the Earth's atmosphere. Friction with the atmosphere causes the debris to explode and burn, generating the streak of light. When the Earth passes through the debris trail left by a comet MANY meteors can be seen, referred to as a "meteor shower"
• Meteorite- a piece of rock that survives its trip through the Earth's atmosphere and actually makes contact with the Earth's surface.
• There are two types of meteorites.
• Stone or Rocky - made of silicate rock materials
• Metal - made mainly of nickel and iron
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