Exploration of Mars
The Viking program launched "Viking 1" and "Viking 2" spacecraft to Mars in 1975; The program consisted of two orbiters and two landers – these were the first two spacecraft to successfully land and operate on Mars.
The primary scientific objectives of the lander mission were to search for biosignatures and observe meteorologic, seismic and magnetic properties of Mars. The results of the biological experiments on board the Viking landers remain inconclusive, with a reanalysis of the Viking data published in 2012 suggesting signs of microbial life on Mars.
The Viking orbiters revealed that large floods of water carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Areas of branched streams, in the southern hemisphere, suggest that rain once fell.
Mars landing
The Mars Science Laboratory (MSL) (and Curiosity rover), launched in November 2011, landed on Aeolis Palus, between Peace Vallis and Aeolis Mons ("Mount Sharp"), in Gale Crater on Mars on August 6, 2012, 05:17 UTC. The landing site was in "Quad 51" ("Yellowknife") of "Aeolis Palus" near the base of "Aeolis Mons". The landing site was less than from the center of the rover's planned target site after a journey. NASA named the landing site "Bradbury Landing", in honor of author Ray Bradbury, on August 22, 2012.