Mars

Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. It is a terrestrial planet with a thin atmosphere and a solid surface. Mars measures about half the diameter and one-tenth the mass of Earth. Its day length is 24 hours 37 minutes, close to Earth’s, and its year spans about 687 Earth days. The planet has seasons, polar ice caps, and weather that includes dust storms that can wrap around the globe.

Surface features include Olympus Mons, the tallest volcano and shield volcano in the Solar System, and Valles Marineris, a canyon system several thousand kilometers long. The crust shows extensive evidence of past volcanism and impact events. Mars' geology and history suggest it once hosted more substantial liquid water on its surface. The planet today has a thin carbon dioxide–rich atmosphere, about 95% CO2, with surface pressure less than 1% of Earth’s. Water ice exists at the poles and possibly beneath the surface in certain regions.

Mars has two small moons, Phobos and Deimos, likely captured asteroids. The planet’s weak magnetic field allows solar wind to strip its atmosphere over time. Human missions are planned, and robotic missions by NASA, ESA, Roscosmos, CNSA, ISRO, and others have studied the planet extensively. Rovers such as Spirit, Opportunity, Curiosity, and Perseverance have examined rocks and soils, while the Ingenuity helicopter demonstrated powered flight on another world. Future goals include sample return and possible human exploration, as well as the search for past or present life.