Viking 1 was the NASA spacecraft that landed on Mars in July 1976 during the United States Bicentennial year.
Viking 1 consisted of an orbiter and a lander. The lander touched down in Chryse Planitia on July 20, 1976, becoming the first U.S. spacecraft to land successfully on Mars and return images from the planet's surface. The orbiter had already entered Martian orbit and helped relay data and photographs.
The landing date was especially memorable because NASA had originally considered July 4, the Bicentennial's central date, for the landing. The actual touchdown occurred on July 20, which was also the seventh anniversary of Apollo 11's first human landing on the Moon.
Viking 2 later landed on Mars in September 1976, so the two missions are often mixed up. Viking 1 and Viking 2 were separate spacecraft launched in the same year, and both carried experiments designed to study the Martian environment and search for possible biological activity.