What Are the Inner Planets?
The inner planets — Mercury, Venus, Earth, and Mars — are called terrestrial planets. They are:
Small
Dense
Made mostly of rock and metal
Located close to the Sun
Mercury – The Extreme World
Closest planet to the Sun
No significant atmosphere
Temperatures range from -180°C to 430°C
A year lasts just 88 Earth days
Venus – Earth’s Twin Gone Wrong
Similar size to Earth
Thick carbon dioxide atmosphere
Surface temperature ~465°C
Crushing atmospheric pressure
Venus demonstrates what a runaway greenhouse effect looks like.
Earth – The Goldilocks Planet
Earth sits in the habitable zone, where liquid water can exist.
Key features:
Liquid oceans
Protective magnetic field
Stable atmosphere
Active geology
Mars – The Red Planet
Cold, thin atmosphere
Evidence of ancient rivers and lakes
Home to Olympus Mons (largest volcano)
Target for future human missions
Key Takeaways
Inner planets are rocky and dense
Earth is uniquely balanced
Mars holds clues to past habitability