Mars

Mars is the fourth planet from the Sun and the second-smallest planet in the solar system after Mercury. Known as the 'Red Planet' due to iron oxide (rust) on its surface giving it a distinctive reddish appearance, Mars has captivated human imagination for centuries and remains the most actively explored world beyond Earth. With a thin carbon dioxide atmosphere and surface pressure about 0.6% that of Earth, Mars is a cold, arid desert world with temperatures averaging about -65°C. Mars is home to the tallest known mountain in the solar system, Olympus Mons, a shield volcano standing about 21.9 km above the surrounding terrain -- nearly three times the height of Mount Everest. The planet also features Valles Marineris, a vast system of canyons stretching over 4,000 km long, up to 200 km wide, and up to 7 km deep. Evidence of ancient river valleys, lake beds, and mineral deposits formed by water strongly suggests that Mars once had a warmer, wetter climate billions of years ago. Mars has two small, irregularly shaped moons -- Phobos and Deimos -- which are thought to be captured asteroids. The planet is a primary target for human exploration, with multiple rovers (including Curiosity and Perseverance) and orbiters currently studying its surface and atmosphere. NASA's Perseverance rover, which landed in Jezero Crater in 2021, is collecting samples for a future Mars Sample Return mission that could provide definitive answers about ancient Martian life.