| When the planets formed 4.6 billion years ago, they formed from an agglomeration of many planetesimals, or small solid celestial bodies. |
| Because they were formed in two very different areas, the planetesimals in the two belts have different compositions. |
| Planet cores and terrestrial rocky planets would accrete from the planetesimals. |
| Although planets, moons and planetesimals may seem to be very different astronomically, their common origin shows that this is not so. |
| The Kuiper belt and Oort cloud are populations of icy planetesimals located beyond the orbit of Neptune. |
| Like the hills and valleys on a contour map the gravity wells of suns, planets, moons, and planetesimals showed up. |
