1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Chapter 4 Section 5 Small Bodies in the Solar System

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Explain why comets, asteroids, and meteoroids are important to the study of the formation of the solar system. Describe the similarities of and differences between asteroids and meteoroids. Explain how cosmic impacts may affect life on Earth. Objectives

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Comets What Is a Comet? A small body of ice, rock, and cosmic dust loosely packed together is called a comet. Comet Tails When a comet passes close enough to the sun, solar radiation heats the ice so that the comet gives off gas and dust in the form of a long tail.

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Structure of a Comet The main parts of a comet are the nucleus, the coma, and the tail. Most comets have two tails—a bluish gas tail and a white dust tail.

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Comet Orbits Most comets revolve around the sun in very long, narrow orbits. Gas and dust tails form as the comet approaches the sun.

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Comet Hale-Bopp On July 23, 1995, two amateur astronomers made an exciting discovery. A new comet, Comet Hale- Bopp, was headed toward the Sun. Larger than most that approach the Sun, it was the brightest comet visible from Earth in 20 years.

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Structure of Comets As a comet approaches the Sun, it changes. Ices of water, methane, and ammonia vaporize because of the heat from the Sun, releasing dust and bits of rock.

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 The gases and released dust form a bright cloud called a coma around the nucleus, or solid part, of the comet.

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 The solar wind pushes on the gases and dust in the coma, causing the particles to form separate tails that point away from the Sun. After many trips around the Sun, most of the ice in a comet's nucleus has vaporized. All that's left are dust and rock, which are spread throughout the orbit of the original comet.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Comet Movement Comets have a predictable revolution. Halley’s comet has a period of revolution of 76 years. It will reappear every 76 years, passing within the view of Earth.

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Comet Origins There are two places where comets originate: –Kuiper Belt – comets with short periods of revolution (named after Gerald Kuiper). The Kuiper belt is just beyond the Solar System. –Oort Cloud – comets with a long period of revolution (named after Jan Oort). The Oort Cloud is much farther away from the Solar System.

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Oort Cloud Astronomer Jan Oort proposed the idea that billions of comets surround the solar system. This cloud of comets, called the Oort Cloud, is located beyond the orbit of Pluto. Oort suggested that the gravities of the Sun and nearby stars interact with comets in the Oort Cloud.

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Asteroids An asteroid is a piece of rock similar to the material that formed into the planets. Most asteroids are located in an area between the orbits of Mars and Jupiter called the asteroid belt.

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Other asteroids are scattered throughout the solar system. They might have been thrown out of the belt by Jupiter's gravity. Scientists monitor the positions of these asteroids. However, it is unlikely that an asteroid will hit Earth in the near future.

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Asteroids Types of Asteroids Asteroids vary in size, shape, and composition. Three asteroids are shown below.

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Exploring Asteroids The sizes of the asteroids in the asteroid belt range from tiny particles to objects 940 km in diameter. Ceres is the largest and the first one discovered. The next three in order of size are Vesta (530 km), Pallas (522 km), and 10 Hygiea (430 km).

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4Asteroids ~5,000 asteroids are discovered every month for a total of 385,000 as of 2007 Estimates calculate over 1 million asteroids larger than 1 km in diameter

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 NEAR On February 14, 2000, the Near Earth Asteroid Rendezvous (NEAR) spacecraft went into orbit around the asteroid 433 Eros and successfully began its one-year mission of data gathering. On February 12, 2001, NEAR ended its mission by becoming the first spacecraft to land softly on an asteroid.

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Asteroids, Meteors, and Comets The NEAR probe marked the first landing on an asteroid (Eros, 30 km long) in 2000.

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 otentially azardous steroids Potentially Hazardous Asteroids Most asteroids remain between Mars and Jupiter. P.H.A.’s come within 7,500,000 km of Earth and are greater than 150 meters in diameter There are currently 931 known P.H.A.’s On average, an asteroid or comet capable of threatening civilization will strike the Earth less than once in 100,000 years according to the Torino Impact Hazard Scale

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Shoemaker-LevyShoemaker-Levy impact 1994

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 What killed the Dinosaurs?

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Meteoroids What Are Meteoroids? A meteoroid is a small, rocky body that revolves around the sun. Meteor Showers You can see a large number of meteors during a meteor shower as Earth passes through the dusty debris of comets. Types of Meteorites Meteorites have different compositions. The three major types of meteorites are stony, metallic, and stony- iron meteorites.

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Meteoroids, Meteors, and Meteorites The small pieces from the comet's nucleus spread out into a loose group within the original orbit of the comet. These pieces of dust and rock, along with those derived from other sources, are called meteoroids.

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Meteoroids, Meteors, and Meteorites Most meteoroids are so small that they completely burn up in Earth's atmosphere. A meteoroid that burns up in Earth's atmosphere is called a meteor.

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Meteor Showers Each time Earth passes through the loose group of particles within the old orbit of a comet, many small particles of rock and dust enter the atmosphere. Because more meteors than usual are seen, the event is called a meteor shower.meteor shower

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 When a meteoroid is large enough, it might not burn up completely in the atmosphere. If it strikes Earth, it is called a meteorite. Most meteorites are probably debris from asteroid collisions or broken-up comets, but some originate from the Moon and Mars.

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Perseid Fireball - August 2006

31. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Shooting Stars and Meteor Showers A meteor passing through our atmosphere is often called a shooting star. They have nothing to do with stars. A meteor shower occurs when Earth passes through the debris left behind by a comet resulting in up to 600 meteors per hour. Named after the constellation that they appear to originate from.

32. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Engraving of Leonid Meteor Shower 1833 Why wouldn’t a meteor shower be as brilliant today?

33. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Review - Meteoroids, Meteors and Meteorites A meteoroid is a piece of debris about to enter Earth’s atmosphere. When entering, it becomes a meteor. Most meteors do not reach Earth, but are burned up in the atmosphere. A meteor that reaches the ground is called a meteorite.

34. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4

35. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Meteor Crater - Arizona Why is this crater incorrectly named?

36. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 What’s the difference? Asteroid: A relatively small, inactive body, composed of rock, carbon or metal, which is orbiting the Sun. Comet: A relatively small, sometimes active object, which is composed of dirt and ices. Comets are characterized by dust and gas tails when in proximity to the Sun. Far from the Sun it is difficult to distinguish an asteroid from a comet.

37. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 Meteoroid: A small particle from an asteroid or comet orbiting he Sun. Meteor: A meteoroid that is observed as it burns up in the Earth's atmosphere - a shooting star. Meteorite: A meteoroid that survives its passage through the Earth's atmosphere and impacts the Earth's surface.

38. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4 The Role of Impacts in the Solar System Future Impacts on Earth? Scientists estimate that impacts that are powerful enough to cause a natural disaster might happen once every few thousand years. The Torino Scale The Torino scale is a system that allows scientists to rate the hazard level of an object moving toward Earth.

39. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4

40. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 4