Inner Planets
Mercury, Venus, Earth and Mars are small and rocky.
About this topic
The inner terrestrial planets are small, dense and rocky with metal cores. Mercury is closest, airless and extreme in temperature; Venus has a thick CO₂ atmosphere creating a runaway greenhouse effect with surface temperatures of about 465 °C; Earth is the only known planet with liquid water on its surface and life; Mars is cold and dry with a thin atmosphere, polar ice caps and the giant volcano Olympus Mons.
Evidence suggests Mars once had liquid water, so rovers search for signs of ancient life.
A useful comparison shows how different the four rocky worlds are despite similar composition. Mercury has almost no atmosphere, so daytime reaches about 430 degrees C and night falls to about minus 180 degrees C. Venus, though farther from the Sun, is hotter than Mercury because its CO2 blanket traps heat, a warning case study for climate science. Mars has a day length close to Earth's (24.6 hours) and seasons, but its air pressure is under one percent of ours.
Studying these neighbours helps us understand Earth: Venus teaches about greenhouse extremes, Mars about lost water and climate change. Rovers such as Curiosity and Perseverance drill rocks and cache samples for return to Earth. A common error is to say the closest planet is the hottest; Venus wins that title. Also remember that Earth's position in the habitable zone is not enough by itself; its size, magnetic field and atmosphere all matter for keeping water liquid.
Key ideas
- Venus has a runaway greenhouse effect
- Mars has ice caps
- Earth has liquid water
Quick check
Use cases: where Inner Planets helps
- Homework: review the key idea behind Inner Planets before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Inner Planets without notes.
- Visual learning: play with the interactive lab to see how Inner Planets changes when you adjust its inputs.
- Teaching a friend: explain Inner Planets in your own words, then compare your version with the key ideas.
Earth science helps with weather forecasts, natural hazards, energy and climate planning.
Frequently asked questions
What is Inner Planets?
Mercury, Venus, Earth and Mars are small and rocky.
What will I learn in Inner Planets?
Venus has a runaway greenhouse effect. Mars has ice caps. Earth has liquid water.
Is Inner Planets part of Earth & Space?
Yes. It is one of 60 Earth & Space topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Inner Planets lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Inner Planets?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.