* Mercury

* Venus

* Earth

* Mars

They are called "inner planets" because they orbit closer to the Sun than the outer planets (Jupiter, Saturn, Uranus, and Neptune).

Here are some key characteristics of the inner planets:

* Small and rocky: They are relatively small compared to the gas giants and are primarily composed of rock and metal.

* Have few or no moons: Earth has one moon, Mars has two tiny moons, while Mercury and Venus have none.

* Thin or no atmospheres: Except for Earth, the atmospheres of the inner planets are thin or nonexistent, making them unable to hold onto heat effectively.

* Solid surfaces: They all have solid surfaces that can be explored with probes and landers.

Let me know if you'd like to learn more about any of the inner planets!