Viking 1 made the first successful soft landing on Mars during the 1976 Bicentennial year.
NASA's Viking 1 lander touched down in Chryse Planitia on July 20, 1976. The mission had originally been considered for a July 4 landing, which would have coincided with the United States Bicentennial, but the landing was delayed after orbital images showed that the planned site was too rough.
Viking 1 carried scientific instruments that photographed the surface, measured atmospheric and soil properties, and conducted biology experiments. Its orbiter entered Mars orbit on June 19, 1976, before the lander descended.
Viking 2 also landed successfully, on September 3, 1976, but it was not first. Mariner 9 orbited Mars without landing, while Mars Pathfinder arrived much later, in 1997. Viking 1 therefore links a major space milestone directly to the year of the United States Bicentennial.