What would happen if a planet were hit by a large object that slowed it down? Would it have a different orbit or would it spiral into the Sun? [As long as the planet didn't directly hit the Sun, it would go into a different stable orbit.] What would happen to an orbit of a planet if it were traveling through a medium that caused the planet to gradually slow down? [The planet would spiral into the Sun. This doesn't happen in our solar system because there is no friction in empty space.] In which direction does the gravity vector always point? Try to create a series of orbits that are nearly circular. How does the speed of the planet relate to its distance from the Sun? Why is this true? [The closer the planet is to the Sun, the faster it must go to maintain a nearly circular orbit.] . How does the mass of the Sun affect the speed of a planet in orbit? If the Sun mass and Planet mass are set to medium, can you create an orbit that has an orbital radius close to 1 AU? What is the period of this orbit? [This orbit is similar to Earth's orbit and has a period close to 1 Earth year.] As a planet orbits the Sun, does the Sun move? [To investigate this question, have students set the Sun mass to small, the Planet mass to large, and click Play. Students can then zoom in on the Sun as much as possible to see its motion, which is an ellipse that has the same shape as the planet's orbit.]