Explaining The Universe on Instagram: "Mars is the fourth planet from the Sun and is often called the “Red Planet” because of its iron oxide–rich soil, which gives it a rusty appearance. It’s about half the size of Earth, with weaker gravity (around 38% of Earth’s) and a thin atmosphere made mostly of carbon dioxide, which makes the surface cold and unable to support liquid water for long periods today. However, scientists have found evidence that rivers, lakes, and perhaps even oceans once exis