Viking 1
Viking 1 was the first of two spacecraft (along with "Viking 2") sent to Mars as part of NASA's Viking program. On July 20, 1976, it became the second spacecraft to soft-land on Mars, and the first soft lander to successfully perform its mission. (The first spacecraft to soft-land on Mars was the Soviet Union's Mars 3 on December 2, 1971, which stopped transmitting after 14.5 seconds.) "Viking 1" held the record for the longest Mars surface mission of days (over 6¼ years) or Martian solar days, until that record was broken by "Opportunity" on May 19, 2010.
Mars landing
In 1976 the two American Viking probes entered orbit about Mars and each released a lander module that made the first fully successful soft landing on the planet's surface. The two missions returned the first color pictures and extensive scientific information. Measured temperatures at the landing sites ranged from 150 to 250 K (-125 to -25 °C), with a variation over a given day of 35° to 50°. Seasonal dust storms, pressure changes, and movement of atmospheric gases between the polar caps were observed. A biology experiment produced possible evidence of life, but it was not corroborated by other on-board experiments.