A rocky planet has a solid outer surface. Earth and Mars are examples. Giant planets are much larger and have deep outer layers of gas. A cloudy sky does not make a planet a gas giant: rocky Venus has a thick atmosphere too.
Space · Discover & try
What makes a planet rocky or giant?
Reading level 1 of 5 · EarlyChange
Word help
Terrestrial
A rocky planet such as Earth or Mars.
Gas giant
A giant planet dominated by hydrogen and helium.
Ice giant
A giant with a larger fraction of heavier compounds; not a ball with a frozen outer surface.
Watch · Try · Explain
See how it works
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Original conceptual cutaways; layer fractions and planet sizes are not to scale.
What to look for
- Compare surface with atmosphere.
- Compare the two giant categories.
- Look for a rocky world with thick clouds.
Explain what you noticed
A newly described planet has a solid rocky surface beneath a thick atmosphere. Which conclusion follows?
Keep this idea: A planet’s composition and structure matter more than its colour.
Follow the sources
Source material checked 2026-10-28. Explanations and activities by Nepedia. Source links do not imply endorsement.
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