Explaining The Universe on Instagram: "Mars is the fourth planet from the Sun and is often called the Red Planet because iron oxide (rust) in its soil gives it a reddish color. It’s a cold, dry world with a thin atmosphere made mostly of carbon dioxide, surface temperatures averaging about −60 °C, and gravity roughly 38% of Earth’s. Mars has some extreme geology, including Olympus Mons, the largest volcano in the solar system, and Valles Marineris, a canyon system far larger than the Grand Canyo