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.
Opportunity mission timeline
Opportunity, MER-B (Mars Exploration Rover – B), is a robotic rover active on the planet Mars since 2004. Launched on July 7, 2003, "Opportunity" landed on Mars' Meridiani Planum on January 25, 2004 at 05:05 Ground UTC (about 13:15 Mars local time), three weeks after its twin "Spirit" (MER-A), also part of NASA's Mars Exploration Rover Mission, touched down on the other side of the planet. While "Spirit" became immobile in 2009 and ceased communications in 2010, "Opportunity" remains active as of December 11, 2017, having already exceeded its planned 90 sol (Martian days) duration of activity by (in Earth time). "Opportunity" has continued to move, gather scientific observations, and report back to Earth. What follows is a summary of events during its continuing mission.