1. 7.5 Other Objects In the Solar System (Pages 297-306) Homework: Page 306 # 1, 3, 7, 8 Key Concepts: (Page 306)

2. In addition to planets, the solar system contains many different objects, such as dwarf planets, asteroids, comets and meteors. There is a very real danger that an asteroid or a large meteor will hit Earth again, The Canadian Space Agency and Canadian businesses are building a satellite that will help to detect near-Earth objects that could be harmful if they hit Earth.

3. Copyright © 2010 McGraw-Hill Ryerson Ltd. In addition to the Moon and planets, other important objects in the solar system include comets, meteoroids, and asteroids. 7.5 Other Objects in the Solar System Comets are composed of rocky material, ice, and gas that originate in the Kuiper Belt and the Oort Cloud. The Kuiper Belt is a disc-shaped group of millions of small objects orbiting the Sun beyond the orbit of Neptune (trans-Neptunian objects) (Page 297)

4. Copyright © 2010 McGraw-Hill Ryerson Ltd. Visualizing the Kuiper Belt (Page 298)

5. Copyright © 2010 McGraw-Hill Ryerson Ltd. In 2006, the IAU demoted Pluto to dwarf planet status because its orbit sometimes crosses Neptune’s orbit. The Plight of Pluto Other Kuiper Belt objects, such as the dwarf planet Eris, are actually larger than Pluto. (Page 299)

6. Copyright © 2010 McGraw-Hill Ryerson Ltd. The Oort Cloud The Oort Cloud is a spherical cloud of icy fragments of debris 50 000 to 100 000 AU from the Sun. This region is thought to be home to many comets. It marks the outer boundary of the Sun’s gravitational influence. Wikipedia/AZcolvin 429 (Page 299)

7. Copyright © 2010 McGraw-Hill Ryerson Ltd. Most comets originate in the Kuiper Belt and the Oort Cloud. Occasionally Jupiter’s gravitational influence will nudge a comet to change its orbit and enter the inner solar system. Comets While some comets visit the Sun just once, periodic comets orbit the Sun. When a comet comes too close to the Sun, the radiation from the Sun causes it to release gases and particles, forming a tail that always points away from the Sun. Periodic Comets (Pages 299-300)

8. Copyright © 2010 McGraw-Hill Ryerson Ltd. Asteroids Asteroids are small, non-spherical objects that range in size from a tiny speck, like a grain of sand, to 500 km wide. Most asteroids originate in the asteroid belt between Mars and Jupiter. They are believed to be composed of debris left over from the formation of the solar system. Asteroids can have their own moons, as shown in the image above. Asteroid Ida Moon Dactyl (Page 300)

9. Copyright © 2010 McGraw-Hill Ryerson Ltd. Meteoroids, Meteors, and Meteorites The most famous meteor shower is the Perseid meteor shower, which occurs around August 12 every year. It results from Earth passing through debris left along the path of Comet Swift Tuttle. A meteoroid is a piece of rock moving through space, while a meteor is a meteoroid that hits Earth’s atmosphere and burns up. Meteorites are meteoroids that are large enough to pass through Earth’s atmosphere and reach the ground without being totally burned up. (Page 301)

10. Copyright © 2010 McGraw-Hill Ryerson Ltd. Asteroid and Meteor Impacts An asteroid the size of a mountain hit Earth 65 million years ago. Many scientists believe that this impact led to climate changes that resulted in the global mass extinctions of thousands of species. Impact craters in Nunavut (A) and in Arizona (B) are evidence of impacts many years ago. (Page 302)

11. Copyright © 2010 McGraw-Hill Ryerson Ltd. Tunguska Devastation A more recent impact occurred on June 30, 1908, in Tunguska, Siberia, when an object entered Earth’s atmosphere and destroyed an area of more than 2000 km 2. The object (thought to be about 50 m in diameter) flattened nearly 100 million trees and killed thousands of forest animals. Many astronomers around the world are currently working to discover and map the courses of any Near Earth Objects (NEOs) that could pose an impact risk to Earth. In 2010, Canada will launch NEOSSat to help find NEOs. (Page 303)