The correct answer is option 2: Earth. Earth is often referred to as the "Blue Planet" because approximately 71% of its surface is covered in water. This extensive water coverage gives the planet a distinct blue appearance when viewed from space.

Option 1, Saturn, is a gas giant planet known for its captivating rings, but it is not referred to as the "Blue Planet."

Option 3, Jupiter, is also a gas giant planet, but it is known for its vibrant bands of clouds and its iconic Great Red Spot, rather than being called the "Blue Planet."

Option 4, Mars, is often called the "Red Planet" because of its reddish appearance, mainly due to the iron oxide present on its surface. Therefore, it is not the correct answer for being called the "Blue Planet."