Planet families: compare, then classify

A family is a comparison

Knowing the planet order is useful, but order is not the only way to compare worlds. Today we group planets by broad properties. Members of a group share features without being identical. A family label is a starting point for questions, not the end of exploration.

Begin with rocky worlds

Mercury, Venus, Earth and Mars belong to the terrestrial group. Terrestrial planets have rocky surfaces. The word does not mean that they all have Earth's weather or living things. Four names share a category, but each planet still has its own story.

Two kinds of giant planet

Jupiter and Saturn are gas giants. Uranus and Neptune are ice giants. All four are giant planets, but our table separates two subgroups. The name ice giant does not promise a solid frozen skating rink. Keep the scientific category separate from a picture invented by the name.

Read the purpose of the picture

The boxes organize names, not actual sizes. A planet in a larger box is not automatically larger than one in a smaller box. To compare diameters, we would need measurements or a labeled size scale. Always ask which property a diagram is designed to show.

Pause: classify three cards

Here are three planet cards: Mars, Jupiter and Neptune. Pause and choose the one that belongs to the terrestrial group. Then explain why the other two can share the broad giant category without belonging to the same giant subgroup. Use properties and the classification we learned.

Check both levels of grouping

Mars is terrestrial. Jupiter is a gas giant and Neptune is an ice giant. Saying that Jupiter and Neptune are both giants is true in this grouping, but saying they belong to the same subgroup would lose a useful distinction. Categories can have smaller categories inside them.

Saturn has company

Fun fact: Saturn is not the only ringed planet. Jupiter, Uranus and Neptune have rings too, although Saturn's are much easier to notice. A feature can exist even when a simple picture leaves it out. Missing detail in a diagram is not evidence of absence.

Compare with a clear purpose

Continue to the worksheet below the video. Classify planets, count group members and explain what information a size comparison would need. Try drawing the same groups in different arrangements. Changing the layout should not change which planet belongs to which stated category.