Mars is a planet in the Solar System. It is the closest planet to the Earth, and is inhabited by Martians.
Geography and Transportation
In the Calvin and Hobbes universe, Mars is more cartoony than it is in the real universe. It is covered in wacky ridges and cracks as far as the eye can see. It can be reached, unbeknownst to any but Calvin, by using a wagon. It is described as being nothing but "rugged, natural beauty as far as the eye can see".
Calvin and Hobbes grew tired of the constant pollution caused to the Earth and decided to get away from it all by flying to Mars. With the help of their wagon, they were able to make it into outer space and travel all the way there, but they forgot to bring the camera with them. They were just getting used to their new surroundings such as trying to find ways to keep their trash from littering the planet, plugging in a night-light, and noticing that the planet is inhabited by Martians. When they met one, they were terrified of it and vice versa. Seeing as how they didn't want to ruin the Martians' planet, they decided to head back to Earth and get used to all the pollution.