Orbiter , Credit: NASA

The Viking orbiters played several roles. They transported the landers to Mars, communicated with the landers, and also performed their own scientific investigations.

Together, the Viking Orbiters mapped over 97 percent of Mars, taking over 50,000 images. Those images showed large canyons, volcanoes, craters, and evidence of surface water, among other features.

In the summer of 1978, the Viking 2 orbiter was powered down after 706 orbits around Mars. The Viking 1 orbiter ended its run in 1980, after completing over 1400 orbits.