On November 13, 1971, Mariner 9 became the first spacecraft to orbit Mars. [‘On This Day in Space’ Video Series on Space.com](https://www.space.com/39251-on-this-day-in-space.html)

At the time, scientists didn't know much about the Red Planet. NASA had several flybys before Mariner 9. Those flybys showed that Mars had a cratered surface, so some scientists thought that Mars looked just like the moon. Then Mariner 9 blew blew their minds. When Mariner 9 got to Mars, it arrived in the middle of a dust storm. It saw some tall structures sticking through the clouds. When the dust settled, images from Mariner 9 revealed that these structures were the tops of huge volcanoes. One volcano, Olympus Mons, is the tallest in the solar system. Mariner 9 also spotted an enormous canyon called Valles Marineris. This canyon is five times longer than the Grand Canyon in Arizona. Mariner 9 worked for one year in orbit. When it ran out of gas, NASA shut it off. But the spacecraft remains one of the most famous Mars voyagers of all time.