Program 3 Four Rocks near the Sun

After viewing the video and participating in one or more of the Hands-On Activities, students will be able to:
• discuss the similarities and differences between the 4 terrestrial planets of our solar system
• describe the key forces (e.g. size, distance from the Sun, greenhouse effect) which make these worlds different
• recognize "comparative planetology" as the discipline which helps us learn about Earth by looking at other planets

Program Description
Program 3 enables educators to address the 2 key science standards which require students to know the main features of the Earth, (Science Standard 1 "Understands basic features of the Earth"), and the processes which shape our home world and the other planets of our solar system. (Science Standard 2 "Understands basic Earth processes")
• "Features of the Terrestrial Planets" (4:19) uses a simple video checklist to introduce some characteristics in which the four terrestrial planets differ: moons, craters, volcanoes and liquid water. Online you can find additional features by which to "compare and contrast" these planets such as length of day and year, presence and kind of "weather" (sulfuric acid "rain" on Venus and "dust-storms" on Mars), and more.
• "What Makes them Different?" (4:21) A look at how planets form and the most important processes which make the terrestrial planets into very different places. These include size and distance from the Sun, which, for example, make Mercury uninhabitable. Size and temperature also drive volcanism, which in turn shapes a planet's atmosphere.
• "Comparative Planetology" (1:17) returns to the theme introduced in Program 1: that while we cannot do controlled experiments to see what may happen to the atmosphere of our planet, we can learn from the histories and current conditions on those most like Earth-Mars and Venus. Comparative planetology may enhance our understanding of such complex issues as global climate change and replace opinion and debate with science.

Chris Chyba uses a down-home example of small and large potatoes in an oven to explain how size is a basic but critical factor in planetary formation and evolution: smaller planets cool faster. Claudia Alexander compares volcanism on Earth, Venus and Mars, and shows how plate tectonics shaped the chain of Hawaiian Islands. By comparing and contrasting how the greenhouse effect has impacted Venus, Earth and Mars, Chyba lucidly explains why liquid water is plentiful on our planet, but has vanished from the surfaces of Venus and Mars. (Please note that, as more fully described in program 4, recent images from the Global Surveyor spacecraft indicate that liquid water may still be able to exist for short intervals on the Martian surface. Yesterday's textbooks cannot keep up with the ongoing process of solar system exploration!) Please note: mathematically observant students may point out that the percentages of nitrogen and oxygen present in Earth's atmosphere shown in the program do not total 100%. Additional constituents include argon, carbon dioxide and smaller amounts of several other gases.