Mars, also known as the red planet, is the fourth planet away from the sun. Mars has an atmosphere composed of carbon dioxide and is very thin. Mars is home to the tallest mountain in the universe. Olympus Mons, located on mars, Is about 21 kilometers tall, and is a shield volcano. Mars has a red tint because of a mineral called iron oxide that is very common on the surface of mars. mars has two polar ice caps, one at its north pole and one at its south pole. Both ice caps are mainly composed of water. A year on mars usually lasts for about 1 year and 320 days, while a day on mars last for about 24 hours and 39 minutes.