Mars is a small and rocky planet with a thin atmosphere that’s mostly made of carbon dioxide. It’s got a lot of fascinating features, including the largest volcano in the solar system (Olympus Mons) and a canyon system that’s longer than the entire United States (Valles Marineris). Scientists have been studying Mars for decades, using orbiters, rovers, and landers to learn more about its geology, climate, and potential for life. There’s even evidence that Mars had liquid water on its surface in the past, which raises the possibility that life may have once existed there. There are also plans to send humans to Mars in the coming decades, which could be an important step towards establishing a permanent human presence beyond Earth.