1. Asteroids, Meteors, and Comets

2. What are they? How are they different from each other?

3. Comets Comets are really just gigantic dirty snowballs!

4. Composition Water Ice Carbon Dioxide Ice Ammonia, Methane Rocky and Metallic Materials Halley’s Comet

5. Comets orbit the sun in VERY elliptical paths. Some comets have short period orbits (as short as 3 years) But some comets have periodicities of hundreds of thousands of years!

6. Comets are relatively small (several kilometers in diameter). Most come from the Oort Cloud beyond the orbit of Pluto. The Oort Cloud is really, really far away! (~100,000AU)

7. As a comet nears the sun, solar energy vaporizes frozen gases, forming a glowing "head" called a coma.

8. The comet also develops a tail of ionized gases and dust that may be millions of km long.

10. Comets have no light of their own, they reflect sunlight.

11. Meteors, Meteorites, and Meteoroids A meteor is a shooting star. Particles glow as they enter the atmosphere.

12. A meteorite is a meteor that hits the ground.

13. A meteroid is the object before it enters the atmosphere. (It is like an asteroid but smaller)

14. Meteor Composition: Stony Iron Stony Iron 5% 94% 1%

15. Meteorite Hunters! http://www.youtube.com/watch?v=xsCsdrQGOKw http://www.youtube.com/watch?v=C11zJIJrX-s&feature=related Which type of meteorite do you think is easiest to find? Why?

16. Meteorite Facts: Meteorites are around 4.5 billion years old. Astronomers study meteorites because they represent primitive materials from the days of solar system formation. 37,000 – 78,000 tons of meteoric material fall to Earth each year (most is microscopic) Largest: 34 tons, NY Museum of Natural History.

17. Damage from meteorites? Property damage has been documented Personal injury has been reported since ancient times but is not well documented.

18. Asteroids Same types as meteoroids Most are located in the asteroid belt between Earth and Mars. ~ 10,000 have been identified. Largest is Ceres. Some asteroids have their own moon!

19. Tunguska Event One hundred years ago an asteroid of about 220 million pounds entered Earth's atmosphere above Siberia at a speed of about 33,500 miles per hour. It never hit the ground. Instead it heated the air around it to about 44,500 degrees Fahrenheit and exploded at an elevation of about 28,000 feet. The energy produced was nearly 200 times more powerful than the Hiroshima bomb.

20. http://www.youtube.com/watch?v=EiXpp-i442s

21. Chicxulub Event The Chicxulub crater was formed when an asteroid struck on the coast of the Yucatan Peninsula. Most scientists agree the impact played a major role in the "KT Extinction Event" that caused the extinction of most life on Earth, including the dinosaurs.

22. 112 mile diameter crater. Location

23. Why did the dinosaurs die from this? The impact vaporized tons of rock and earth. It caused shock waves that flattened forests up into Canada Dense clouds of dust blocked the sun’s rays which killed plants and lowered temperatures. Eventually up to 70% of the species on Earth died off.

24. How do we know? Iridium layer (rare on Earth but common in asteroids). Melted rock. Fractured crystals. Fossil record.

25. NEO Near Earth Objects Any asteroid within 1.3 AU miles of Earth Currently there are 7837 that scientists are watching. (as of 2/27/11)

26. PHA Potentially Hazardous Asteroids Asteroids that may pass within 0.05 AU of Earth (4,650,000 mi.) Scientists are tracking 1204 PHA (as of 2/27/11)

28. http://www.pbs.org/wgbh/nova/s pace/asteroid.html