Forty years ago, NASA made its first soft landing on Mars. The space agency sent down the Viking 1 lander on July 20, 1976 after a little bit of drama -- when the spacecraft arrived it was discovered the original landing site was too rocky to support a safe landing. This pushed back the landing date from July 4, which was supposed to coincide with bicentennial celebrations back on Earth.
But the patience was worth it, as Viking 1's lander lasted six years on the surface and transmitted back valuable data about the Martian surface, including its atmosphere, rocks and a bit of Mars history as well. From above, the Viking 1 orbiter sent back thousands of images of the Red Planet, including evidence of ancient water flows on the surface. Here are some of the most interesting pictures from the mission.