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.
Exploration of Mars
The "Mars Express" mission of the European Space Agency (ESA) reached Mars in 2003. It carried the "Beagle 2" lander, which was not heard from after being released and was declared lost in February 2004. "Beagle 2" was located in January 2015 by HiRise camera on NASA's "Mars Reconnaissance Orbiter" (MRO) having landed safely but failed to fully deploy its solar panels and antenna. In early 2004, the "Mars Express" Planetary Fourier Spectrometer team announced the orbiter had detected methane in the Martian atmosphere, a potential biosignature. ESA announced in June 2006 the discovery of aurorae on Mars by the "Mars Express".