Mars

A rusty desert world

Mars gets its famous red color from iron oxide, essentially rust, in its dust and rocks. Standing on the surface, you would see a butterscotch sky, rocky plains and distant hills under a Sun that looks smaller and dimmer than at home. You would also be freezing: the average temperature is around -60 °C, and the air is so thin, mostly carbon dioxide, that you could not survive without a pressurized suit.

A Martian day, called a sol, is only about 40 minutes longer than ours, but a year lasts 687 Earth days. Mars also has seasons, polar ice caps and dust storms that can occasionally grow to wrap the whole planet.

Blue sunsets on the Red Planet

On Earth, sunsets glow orange and red. On Mars, it is the other way around. Fine dust in the Martian air scatters blue light forward, close to the direction of the Sun, so as the Sun sinks low a cool blue halo forms around it while the rest of the sky stays dusty and tan.

NASA's Curiosity rover captured this effect in color in 2015 from Gale Crater, and it remains one of the most striking reminders that Mars is an alien world, even when its landscapes look familiar.

Giant volcanoes and dried-up rivers

Mars is home to Olympus Mons, the largest volcano known in the solar system, rising about 22 km, roughly two and a half times the height of Mount Everest. Nearby, the Valles Marineris canyon system stretches nearly 4,000 km, about the distance from California to New York.

Orbiters and rovers have found dry riverbeds, ancient lake deltas and minerals that only form in water. Billions of years ago, Mars was warmer and wetter, with a thicker atmosphere. When it lost most of its magnetic field, the solar wind gradually stripped much of that air away, and the planet dried and cooled.

Mars also has two tiny, lumpy moons, Phobos and Deimos, which may be captured asteroids or debris from an ancient impact. Phobos orbits so low that it circles Mars about three times a day and is slowly spiraling inward. In tens of millions of years it will likely break apart or crash into the planet.

A planet run by robots

No planet besides Earth has been explored as thoroughly. Viking 1 sent the first long-lived images from the surface in 1976, followed by rovers such as Sojourner, Spirit, Opportunity and Curiosity. NASA's Perseverance rover landed in Jezero Crater in February 2021 and is collecting rock samples from an ancient river delta, searching for signs of past microbial life.

It carried a passenger, too: the Ingenuity helicopter, which made the first powered, controlled flight on another planet in April 2021 and went on to fly dozens of times.

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