After orbiting Mars for more than a month and returning images used for landing site selection, the orbiters and landers detached; the landers then entered the Martian atmosphere and soft-landed at the sites that had been chosen. The "Viking 1" lander touched down on the surface of Mars on July 20, 1976, and was joined by the "Viking 2" lander on September 3. The orbiters continued imaging and performing other scientific operations from orbit while the landers deployed instruments on the surface.