What holds the planets in their orbits?
Their momentum and energy. b) The tug of gravity constantly pulling them toward the Sun. c) Collisions with asteroids and comets d) Kepler’s second law. 4. Comet Hale-Bopp has an orbital period of about 4,000 years. However, it was only visible to most people on Earth for a few months. Why could this be? a) We can only see comets standing near the equator. b) The comet melted as it got closer to the Sun. c) Greenhouse gases in the comet (methane, carbon dioxide) prevented us from seeing it. d) An application of Kepler’s second law. 5. The Earth’s atmosphere has been relatively stable over the age of the Solar System. What is one reason why? a) Its orbit has always been an ellipse. b) It is small enough so that it cannot retain an atmosphere for very long. c) People have recently tried to stabilize it by burning fossil fuels. d) There has been feedback between its atmosphere and surface. 6. Put these objects in proper order of size (diameter) a) Milky Way, planet, solar system, star, as
