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.
Rover (space exploration)
The Mars Pathfinder mission included "Sojourner", the first rover to successfully deploy on another planet. NASA, the space agency of the United States, launched Mars Pathfinder on 4 December 1996; it landed on Mars in a region called Chryse Planitia on 4 July 1997. From its landing until the final data transmission on 27 September 1997, Mars Pathfinder returned 16,500 images from the lander and 550 images from "Sojourner", as well as data from more than 15 chemical analyses of rocks and soil and extensive data on winds and other weather factors.