Mars is also known as:

- The Red Planet

Explanation:
Mars, the fourth planet from the Sun in our solar system, is commonly referred to as "The Red Planet". This nickname is derived from its reddish appearance, which is caused by the iron oxide (rust) present on its surface. Let's explore the reasons why Mars is often called "The Red Planet" in more detail.

1. Iron Oxide:
The reddish hue of Mars is primarily due to the presence of iron oxide, or rust, on its surface. The iron in the Martian soil undergoes a process called oxidation, which results in the reddish coloration. This iron oxide gives Mars its distinct reddish appearance, making it stand out among the other planets in our solar system.

2. Composition:
Mars has a rocky surface with a relatively thin atmosphere. The soil and rocks on Mars contain a high concentration of iron, which contributes to its reddish color. The iron oxide particles in the soil reflect sunlight, giving Mars its characteristic red glow.

3. Volcanic Activity:
Volcanic activity on Mars in the past has also played a role in the planet's reddish appearance. Volcanic eruptions released minerals and gases into the atmosphere, altering the surface composition and contributing to the formation of iron oxide. These volcanic processes have shaped the geology of Mars and contributed to its distinctive color.

4. Dust Storms:
Mars is known for its dust storms, which can cover large areas of the planet's surface. During these storms, fine dust particles are suspended in the atmosphere, further enhancing the reddish tint of the planet. These dust storms can last for weeks or even months, enveloping the entire planet and making it appear even redder.

In conclusion, Mars is called "The Red Planet" due to the presence of iron oxide on its surface, its rocky composition, volcanic activity, and dust storms. The combination of these factors gives Mars its distinct reddish appearance, making it easily recognizable in the night sky.