The idea
Eight planets, several dwarf planets, and an enormous number of smaller bodies, all orbiting one star.
| Planet | Type | AU from Sun | Year (Earth years) | Moons |
|---|---|---|---|---|
| Mercury | Terrestrial | 0.39 | 0.24 | 0 |
| Venus | Terrestrial | 0.72 | 0.62 | 0 |
| Earth | Terrestrial | 1.00 | 1.00 | 1 |
| Mars | Terrestrial | 1.52 | 1.88 | 2 |
| Jupiter | Gas giant | 5.20 | 11.9 | 95+ |
| Saturn | Gas giant | 9.58 | 29.4 | 145+ |
| Uranus | Ice giant | 19.2 | 84.0 | 28+ |
| Neptune | Ice giant | 30.1 | 164.8 | 16+ |
The pattern in the table
Rocky and small close in; gaseous and huge farther out. The dividing line is the frost line — beyond it, water and methane could freeze into solids and be swept up by growing planets. Inside it, the young Sun blew those gases away.
Why Pluto was reclassified
The definition of a planet requires that a body has cleared its orbital neighbourhood. Pluto shares its region with countless Kuiper Belt objects. Nothing about Pluto changed — the definition did, once we found how many similar objects were out there.
Build a scale model in Scale Model of the Solar System and the numbers in that table stop being abstract.
Curriculum connection
E2.4
describe major components of the solar system and the universe and compare their characteristics
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E2.5
quantify distances in the solar system and the universe by applying an understanding of relative distances and sizes and using appropriate units of measure
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