Program 6 Small Worlds and Cosmic Collisions

After viewing the video and participating in one or more of the Hands-On Activities, students will be able to:
• list and differentiate the small bodies found in our solar system: comets, asteroids, meteors and meteorites
• discuss why asteroids and comets are important objects of study
• describe several current and future missions to asteroids and comets, such as NEAR and Stardust

Program Description
When we think of the solar system, we tend to focus on planets, or-at most-large moons such as those seen in program 5. But recent missions and discoveries show that "small bodies" can have great importance in understanding the origin and evolution of the solar system. This program is, therefore, on the cutting-edge of new science.
• In "Asteroids and the Birth of the Solar System" (2:27) we track humanity's ever-closer views of asteroids, which appear just as points of light ("star-like" is what "asteroid" means) from the surface of the Earth. First the Galileo mission, and now NEAR, show us that asteroids may be lumpy like potatoes, rather than round like planets. Some of the NEAR "Images of the Day" from the Johns Hopkins Applied Physics Laboratory reveal boulders and craters on the surface of asteroid 433 Eros.
• "Comets in Close Up" (5:33) provides an overview of where in the solar system comets and asteroids are found: the asteroid belt between Mars and Jupiter, the "Jupiter family" of comets, the Kuiper Belt, and the Oort Cloud. Students learn that the planet, Pluto, and Neptune's giant moon, Triton, are thought by some astronomers to be large members of the Kuiper Belt. The program describes what happens when a comet passes close to the Sun, and sometimes even plunge directly into the Sun. Historical images from the Bayeux tapestry (1066 AD) and later, remind us that in the past comets were regarded as omens of bad luck.
• "Cosmic Collisions" (3:09) describes craters on Earth, the Moon, and other planets and moons as evidence of a time of great impacts, including the one, some 65 million years ago, which may have helped cause the dinosaurs to go extinct. Footage from the 1994 collision of comet Shoemaker-Levy 9 with Jupiter reminds us that collisions continue to happen in recent times.

Andy Cheng, project scientist for NEAR, the Near Earth Asteroid Rendezvous Mission, and Claudia Alexander, U.S. project scientist for the future Rosetta mission to a comet, define the key characteristics of asteroids and comets. Both are objects formed long ago when the solar system was young. Asteroids have been shaped by successive collisions and some show evidence of planet-like processes ("differentiation" of layers and core material). Comets, by contrast, are characterized by a larger proportion of ices and frozen gases. When they pass close to the Sun, they heat up and a tail of gas and dust streams back behind them.