# The Rocky Planets

- Link: https://thecuriosi.com/lessons/rocky-planets/
- Published: 2026-10-31T14:56:22+05:30
- Author: MAHENDRA MANCHIKALAPATI

1. [Courses](https://thecuriosi.com/courses/)
 2. [The Solar System and Space](https://thecuriosi.com/courses/solar-system-for-kids/)
 3.  Lesson 3 of 8

The four planets closest to the Sun are called the **rocky planets** or **terrestrial
planets**. They have hard, rocky surfaces you could stand on, if you had a very 
good spacesuit! In this lesson you will visit Mercury, Venus, Earth and Mars.

## Mercury: the smallest and fastest

Mercury is the **closest planet to the Sun** and the **smallest planet**. It zooms
around the Sun in just **88 Earth days**, faster than any other planet.

Mercury has almost no air to hold in heat. In the day it can be hot enough to melt
lead, but at night it becomes freezing cold. Its grey surface is covered in **craters**,
made by space rocks crashing into it. Mercury has **no moons**.

## Venus: the hottest planet

Venus is the second planet from the Sun and is almost the same size as Earth. But
it is a very different place. Venus is covered in thick clouds, and its air is mostly**
carbon dioxide**, which traps heat like a blanket.

This makes Venus the **hottest planet**, about **465 degrees Celsius**, even hotter
than Mercury! Venus also spins very slowly and in the **opposite direction** to 
most planets. Venus has no moons. It is often the brightest point of light in the
night sky after the Moon.

## Earth: our home

Earth is the third planet from the Sun and the only planet we know that has **life**.
Earth is special because:

 * it has **liquid water** on its surface, covering about 70 percent of it
 * its air contains **oxygen** that animals and people breathe
 * it is not too hot and not too cold
 * it has a protective layer of air that shields us from harmful rays

Earth has **one moon**, which we simply call the Moon.

## Mars: the red planet

Mars is the fourth planet. It looks **red** because its soil contains iron that 
has turned to rust. Mars has the tallest volcano known in the solar system, **Olympus
Mons**, which is about two and a half times as tall as Mount Everest.

Mars is colder than Earth and has very thin air. Scientists have found signs that
Mars had rivers and lakes long ago, and there is still ice at its poles. Robots 
called **rovers** are exploring Mars right now. Mars has **two small moons**, Phobos
and Deimos.

### Comparing the rocky planets

  |  Planet |  Moons |  Special fact |  
   |  Mercury |  0 |  smallest and fastest |  
 |  Venus |  0 |  hottest planet |  
 |  Earth |  1 |  only known planet with life |  
 |  Mars |  2 |  red rusty soil and giant volcano |

### Example

Jamal wanted to know why Venus is hotter than Mercury even though Mercury is closer
to the Sun. He learned that Venus’s thick carbon dioxide air traps heat, while Mercury
has almost no air, so its heat escapes.

## Key takeaways

 * The rocky planets are Mercury, Venus, Earth and Mars.
 * Mercury is smallest; Venus is hottest because of its thick air.
 * Earth is the only planet known to have life and liquid water on its surface.
 * Mars is red because of rusty soil, and rovers explore it today.

## Practice

 1. Which rocky planet has two moons?
 2. Why is Venus so hot?
 3. Name two things that make Earth good for life.

Answers: 1 is Mars. 2 is because its thick carbon dioxide air traps heat. 3 could
be liquid water, oxygen, a comfortable temperature or a protective layer of air.

 [Log in](https://thecuriosi.com/wp-login.php?redirect_to=https%3A%2F%2Fthecuriosi.com%2Flessons%2Frocky-planets%2F)
to mark lessons complete and track your progress.

 [ Previous lesson The Sun: Our Star ](https://thecuriosi.com/lessons/the-sun-our-star/)
[ Next lesson The Giant Planets ](https://thecuriosi.com/lessons/giant-planets/)

 [Back to course overview](https://thecuriosi.com/courses/solar-system-for-kids/)

Share this