Starter – have a think!

1. Starter – have a think! Can you think of any potential threats to lifeon Earth from outer space?

2. Objectives • To recall a definition for a comet and an asteroid; • To describe how a comet and an asteroid travels; • To know an example of a comet; • To consider the implications of an asteroid or comet collision on Earth.

3. Meteors, meteorites and asteroids As the Earth moves through space, it collides with lumps of material which burn up in the atmosphere. These are called meteors and can be seen as streaks of light in the night sky. A large meteor may not burn up completely and hits the Earth with a lot of energy. This is called a meteorite. Asteroids are very large rocks that normally orbit the Sun. Sometimes, they break free and collide with planets.

4. Asteroid impact

5. Dinosaurs and asteroid impact In 1990, a scientist called Alan Hildebrand was looking at some old geological data. He found evidence of a crater with a diameter of 100 km, at Chicxulub, Mexico. Could this have wiped out the dinosaurs?

6. What are comets? A ball of ice which travels in very elliptical orbits. The tail only appears when the comet’s orbit takes it nearest to the Sun. Hale-Bopp Comet 1997

7. What is a Near-Earth object? Near-Earth objects(NEOs) are asteroids or comets that pass within a third of the distance of the Earth from the Sun. About 50,000 small NEOs fall on the Earth as meteorites each year without causing much damage. However, it is estimated that around 1000 NEOs are bigger than 1km. The paths of NEOs are monitored by telescopes around the world and the risk of a collision assessed. So far, observations have not found any large NEOs that will collide with Earth.

8. In your notes . . . • Explain what the asteroid belt is, and where it can be found. • Explain the difference between a meter and a metorite. • Define the term ‘global catastrophe’ and give some examples of extraterrestrial bodies which could cause one and how.