Which planet is commonly referred to as the "Red Planet"?

Mars is commonly referred to as the "Red Planet" due to its reddish appearance, which is caused by iron oxide, commonly known as rust, on its surface. This distinctive color makes Mars stand out in the night sky, and it has been observed by astronomers for centuries. The name "Red Planet" has become so ingrained in popular culture that Mars often symbolizes not only the planet itself but also notions of exploration and the possibility of life beyond Earth.

In contrast, Venus, while also a neighboring planet, is often referred to as Earth's "sister planet" due to its similar size and composition, but it does not have the same reddish appearance. Earth, as our home planet, does not fit the description of a red planet at all. Jupiter is known for its massive size and Great Red Spot, a giant storm, but it does not have the same overall red hue associated with Mars. Thus, Mars is the correct answer.