1. Comets, Asteroids, and Meteors

2. Comets The word "comet" comes from the Greek word for "hair.”
Our ancestors thought comets were stars with what looked like flowing hair trailing behind.

3. Comets: “Dirty Snowballs”
Comets are loose collections of ice, dust, and small rocky particles whose orbits are usually very long, narrow ellipses.

4. Structure of a Comet A Comet’s Head
Outer layer= Coma (water vapor, CO2, and other gases)
Solid inner core= Nucleus (frozen ice, gas and dust )

5. Comet’s Tail
As a comet approaches the sun and heats up, some of its gas and dust stream outward, forming a tail.
Most comets have 2 tails:
gas (ion), tail
dust tail
Tails point away from the sun because of the force of the solar wind.
A comet’s tail can be more than 100 million kilometers long.

6. Comet’s Tail

7. Comet’s Orbit
Comets move in an elliptical shaped orbit.

8. Origin of Comets
Most comets are found in 2 regions of the solar system: Kuiper belt and Oort cloud.
Kuiper belt-doughnut-shaped region that extends beyond Neptune’s orbit to about 100 times Earth’s distance from the sun.
Oort cloud-spherical region of comets that surrounds the solar system out to more than 1,000 times the distance between Pluto and the sun.

9. Asteroids A small and rocky space object.
Most asteroids are found in the asteroid belt.
The asteroid belt is located between the orbits of Mars and Jupiter.
Asteroids

11. How many asteroids are there?
There are about 40,000 known asteroids that are over 0.5 miles (1 km) in diameter in the asteroid belt About 3,000 asteroids have been cataloged.
There are many smaller asteroids (100,000).
Asteroids are made of metals, silicate, iron, nickel, and carbon.
The first one discovered (and the biggest) is named Ceres; it was discovered in 1801.
Asteroids range in size from tiny pebbles to about 578 miles (930 kilometers) in diameter (Ceres).

12. ASTEROIDS BECOMING MOONS
Asteroids can be pulled out of their solar orbit by the gravitational pull of a planet. They would then orbit that planet instead of orbiting the Sun.
Astronomers theorize that the two moons of Mars, Phobos and Deimos, are captured asteroids.

13. Asteroid Strike
Scientists hypothesize that one or more large asteroids hit Earth 65 million years ago and caused extinction of the dinosaurs.
Scientists also hypothesize that the largest mass extinction, 250 million years ago, killing off 90% of all species was also caused by a large asteroid.

14. Meteoroids Meteoroid-chunk of rock or dust in space.
Meteoroids come from comets or asteroids.

15. Meteor
When a meteoroid enters Earth’s atmosphere, friction with the air creates heat and produces a streak of light that you can see in the sky.
A meteor is a meteoroid that enters Earth’s atmosphere and burns up.

16. Meteorites
Meteoroids that pass through the atmosphere and hit Earth’s surface are called meteorites.
Classified by composition: stony, iron ,or stony- iron.

17. Video Clip on Meteor Showers
/sci/ess/eiu/meteorshower/index.html
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