World Builders™                                                                         Session One  --  Astronomy       
                         Stable Orbits

                                          for Your Moons


                       Space your moons so that gravity will not pull them into collisions.

     Although planetary systems seem stable, they change over time.  Wandering asteroids occasionally hit planets and moons, and the influence of gravity, while it may work slowly, can cause moons to collide with each other and orbits to change. How can you set up a system that will work long enough for your life forms to flourish?

     Scientists are working with computer models to study orbits and the relationships between planets and moons.  Gravity can affect orbits even at great distances, and with billions of years to work, even small gravitational influences can have power.

     The force of gravity is strongest between objects that are close to each other. Space out your planets and moons!

Check the Roche Limit!

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© 2000, 2003. Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at