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.
2016 in spaceflight
The ExoMars mission, a collaboration between the European and Russian space agencies, was launched on 14 March and reached Mars on 19 October. Dedicated to astrobiology investigations, this flight carried the ExoMars Trace Gas Orbiter, which reached Mars orbit, and the Schiaparelli EDM lander, which crashed upon landing. A subsequent flight scheduled for 2020 will carry the ExoMars rover along with four static surface instruments. 
Meanwhile, the Japanese space probe Akatsuki started its observations of Venus in May after spending five months gradually adjusting its orbit. 
Planetary exploration activities took center stage with the orbit insertion of NASA's Juno probe at Jupiter on 4 July, followed by the launch of NASA's OSIRIS-REx mission to asteroid 101955 Bennu on 8 September. Finally, on 30 September, the Rosetta probe executed a slow crash-landing on comet 67P/Churyumov–Gerasimenko.