Step 1: Understand the term ``Red Planet''.
The planet Mars appears red in the night sky due to the presence of iron oxide (rust) on its surface.
Step 2: Analyze the options.
Venus is known for its thick atmosphere.
Jupiter is the largest planet.
Saturn is famous for its rings.
Mars is called the Red Planet because of its reddish appearance.
Step 3: Conclusion.
Therefore, Mars is known as the Red Planet.