World Builders™                                                                                 Session Two  --  Geology         

    Asteroids and Planetary Spacing 

After many thousands of years your planet will become a world with a solid surface.


     Asteroids are large pieces of minerals and ice that orbit the sun between the orbits of Mars and Jupiter.  As you can see from the pictures, they come in all sorts of shapes and sizes.  Some of them have craters from where they were struck by some other piece of matter.  Astronomers even found one that has a tiny moon orbiting it!

     On this page, and in science fiction movies, the asteroids are very close together.  This is not true in space.  The asteroids are far from one another.  You could drive your spaceship through the asteroid belt without worrying about colliding with one.

   What are the asteroids?  Are they just a belt of space debris, or are they the remains of a planet?

Bode's Law -- A Strange Coincidence?

   A lot of the work in astronomy has been done by mathematicians, because all the splendor of the night sky rests in an invisible web of mathematics.   The mathematicians have discovered many fascinating things about our universe.

     One of the interesting things discovered by mathematicians is the arrangement of spacing of the planets in our solar system, which is called Bode's Law,  or the Titius-Bode Law after the mathematicians who discovered and published it.

     This is how to get the numbers in Bode's Law:


A mathematical formula which generates, with a fair amount of accuracy, the semimajor axes of the planets in order out from the Sun. Write down the sequence
0, 3, 6, 12, 24, ...
and add 4 to each term:
4, 7, 10, 16, 28, ...
Then divide each term by 10. This leaves you with the series
0.4, 0.7, 1.0, 1.6, 2.8, ...
which is intended to give you the semimajor axes of the planets measured in astronomical units.

Bode's law had no theoretical justification when it was first introduced; it did, however, agree with the soon-to-be-discovered planet Uranus' orbit (19.2 au actual; 19.7 au predicted). Similarly, it predicted a missing planet between Mars and Jupiter, and shortly thereafter the asteroids were found in very similar orbits (2.77 au actual for Ceres; 2.8 au predicted). The series, however, seems to skip over Neptune's orbit. The form of Bode's law (that is, a roughly geometric series) is not surprising, considering our theories on the formation of solar systems, but its particular formulation is thought of as coincidental.




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© 1996,1997, 1998, 1999, 2000, 2002, 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 .