Chapter 5: Comets, asteroids, and meteoroids Unit: Earth and Space Systems Chapter 5: Comets, asteroids, and meteoroids

Did you know? The dinosaurs became extinct 65 million years ago. Scientists think that a comet or an asteroid from space hit Earth at that time. Evidence suggests that a crater near Mexico’s Yucatan peninsula is the impact site of an object from space, 10 km in diameter. When the object hit, so much debris was thrown so high into the atmosphere that the skies were dark for several years. Most plants died from lack of sunlight. The affected the entire food web. Animals that ate plants died first and then the animals that ate other animals died. Many of the animals and plants on Earth became extinct.

Activity 1: What are Comets, Asteroids, and Meteoroids? In your group, do research on one of: comets, asteroids, or meteoroids. Prepare a presentation for your class, giving the description, location, orbit (if any), and at least two interesting facts about your celestial object. Include diagrams and pictures in your presentation. As the other groups make their presentations, listen learn, and write notes about the space objects you did not research.

Recording and Reflecting Are comets, asteroids, and meteoroids similar to or different from planets? Explain. Compare comets, asteroids, and meteoroids with each other. How are these objects observed by humans?

Activity 2: Create Craters Spread some newspaper on the floor. Put the dishpan in the centre. Fill the basin with 7 to 10 cm of flour. Before starting your test, practice dropping the rock a few times. Also practice removing it from the flour without disturbing the crater. The tongs might help you remove the rock. Practice measuring the crater without disturbing the sides. Smooth out the flour surface. Use a sifter to sprinkle a small amount of chocolate powder on top of the flour. The contrast of the dark chocolate against the white flour makes it easier to see the craters.

A. Size of meteorite Complete the craters worksheet as you do this activity Drop each rock from the same height. For example, use a meter stick and drop each from a height of 1 meter. Before you drop each rock, predict what will happen to the flour in the dishpan. Measure each crater and record your observations.

B. Speed of Meteorite Choose only one of your three rocks for this test. Put the other two aside, you will not need them Choose three heights from which to drop the rock. Three heights that work well are knee high, shoulder length, and as high as you can reach over your head. Measure each of these heights with a meter stick. Do not throw the rock, just drop it. Measure each crater and record your observations.

Recording and reflecting Complete the Craters Worksheet In your notebook, describe how the size of the object affects the the size of the crater. Describe how the speed of the object affects the size of the crater.

Activity 3: Make a comet Make a scale model of Halley’s comet, using the scale 1cm= 100 000 km. You will need some cotton balls, string, and tape. Tape a cotton ball to the wall. This is the comet’s nucleus and “coma.” Cut 10 pieces of string, each 5 meters long. This is the comet’s tail. Attach each string to the wall, beginning at the cotton ball and then along the wall. Fan out the string slightly. *** The original measurements of the comet are 16 by 8 by 8 kilometers.

Notes A comet is like a dirty snowball with a tail of gas, dust, and debris. The nucleus of a comet is tiny, only a few kilometers in diameter. The coma is the cloud of dust and gas that is given off from the nucleus as the comet nears the sun. The coma is the bright part of the comet we can see from earth. Countless numbers of comets orbit around our sun in very long orbits. The orbits extend far beyond the orbit of Pluto and travel very close to the sun. As the comet approaches the sun, the ice warms up. The gases and dust that were stuck in the ice fly away from the sun forming the coma and tail. The comet’s tail glows from the reflected light, just as light reflects off dust in a sun beam.

Notes The most famous comet is Halley’s comet. Its orbit brings it near earth every 76 years/ Halley’s comet last appeared in 1986.

Notes An asteroid is a small rocky object that orbits the sun. Asteroids range in size from a few meters to several hundred kilometers. Most orbit the sun between Mars and Jupiter, in an area called the asteroid belt. Asteroids are much smaller than planets and usually potato-shaped. The largest known asteroid is 914km across and is named Ceres.

Notes A meteoroid is a small piece of debris, often from a comet or asteroid. Most materials are the size of dust particles. A meteor is the streak of light from a burning meteoroid in Earth’s atmosphere. We often call meteors “falling stars.” but they are not stars at all. Most nights we can see about one meteor every hour. However, Earth sometimes passes through clouds of dust and debris in its orbit around the sun. At these times, we see a “meteor shower”- meteors every two or three minutes.

Notes If a meteoroid is larger than an orange, it might not burn up completely as it passes through earth’s atmosphere. A meteoroid fragment found on Earth’s surface is called a meteorite. Very, very rarely, a comet, asteroid, or large meteoroid hits earth. It would crash with a tremendous, explosive force. The result is a crater- a hole in the ground surrounded by hills from the material thrown in the hole. A famous crater on earth is Meteor Crater in Arizona. The Sudbury Basin in Ontario is also a crater. The moon has many craters because it has no atmosphere to burn up the meteoroids.