Boardworks Ltd Asteroids and Comets

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1 1 of 20 Boardworks Ltd 2011 Asteroids and Comets

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3 What are asteroids? 3 of 20 Boardworks Ltd 2011 Asteroids are large rocks which normally orbit the Sun. Scientists believe that asteroids are debris left over from the formation of the Solar System. Most asteroids are found in the asteroid belt between Mars and Jupiter. Although the asteroid belt looks very dense in images, it is actually mostly empty and several spacecraft have travelled through it safely. The combined mass of all the asteroids within the asteroid belt is only about 4% of the mass of the Moon.

4 Jupiter s gravity I 4 of 20 Boardworks Ltd 2011 The asteroid belt is kept in position because, while the gravity of the Sun is pulling the asteroids inwards, the gravitational field strength of Jupiter is pulling the asteroids outwards. Jupiter s gravity can cause the asteroids in the asteroid belt to accelerate to very high speeds when in orbit, risking collision. Their high kinetic energy means that if the asteroids do collide, they rebound off each other, rather than sticking together and eventually forming new planets.

5 Jupiter s gravity II 5 of 20 Boardworks Ltd 2011 Although it normally protects the inner planets from being continually hit by rogue asteroids, the gravity of Jupiter can cause the orbits of asteroids to wobble so much that eventually they break free and shoot off into space. These asteroids can cross the orbits of other planets, or even collide with them, potentially causing catastrophic damage. The damage that an asteroid hit might cause can be estimated by examining crater sites created by earlier asteroid impacts, both on Earth and on other planets and satellites.

6 Evidence of collisions 6 of 20 Boardworks Ltd 2011 The Earth s surface changes so much that asteroid craters are often no longer visible. Geologists can study rocks under the Earth s surface to find evidence of asteroid collisions in history, including: unusual elements, such as iridium, which are normally found mainly on asteroids sudden changes in the numbers of fossils between layers of rock.

7 True or false? 7 of 20 Boardworks Ltd 2011

8 What killed the dinosaurs? 8 of 20 Boardworks Ltd 2011

9 Class vote 9 of 20 Boardworks Ltd 2011

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11 What are comets? 11 of 20 Boardworks Ltd 2011 Comets are thought to have formed in the outer Solar System, beyond the orbits of the eight planets. They are made from ice and dust and travel in highly elliptical orbits around the Sun. When a comet is close to the Sun, a tail of dust and gas debris may be visible. Comets have been observed for centuries, but it was Edmond Halley in 1705 who first noted the regular appearance of comets. He correctly predicted the arrival of a comet in 1758 Halley s Comet.

12 The orbit of a comet 12 of 20 Boardworks Ltd 2011

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14 What are NEOs? 14 of 20 Boardworks Ltd 2011 Near-Earth objects (NEOs) are asteroids or comets that, during the course of their orbits, enter the neighbourhood of the Earth and have the potential to collide with it. Although most NEOs that collide with the Earth burn up in the atmosphere, an NEO with a diameter of 1 2 km could cause massive damage if it were to hit. As of January 2011, 7661 NEOs had been discovered by NASA. 820 of these have a diameter of 1 km or larger.

15 Observing space 15 of 20 Boardworks Ltd 2011 By making observations of NEOs over time, it is possible to work out their trajectories (paths). It can be difficult to see NEOs because they can be very small and dark in the sky. Humans have observed space for at least the last 5,000 years. Astronomy was revolutionized 400 years ago with the invention of the optical telescope, which enabled astronomers to see light from distant celestial bodies. Optical telescopes are often located in very remote areas, to minimize the effects of light pollution and water vapour.

16 Protecting the Earth 16 of 20 Boardworks Ltd 2011

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18 Glossary 18 of 20 Boardworks Ltd 2011

19 Asteroid or comet? 19 of 20 Boardworks Ltd 2011

20 Multiple-choice quiz 20 of 20 Boardworks Ltd 2011