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.
NASA robots
The Mars rover "Curiosity" is a mobile laboratory that was launched from Cape Canaveral in 2011. The Curiosity landed on Mars surface August 6, 2012. This was the largest rover NASA has put on Mars, being twice as long and five times as heavy as its processors. Despite the extra size the Curiosity took many design elements from the previous generation of Mars rovers such as six wheel drive, rocker-bogie suspension, and cameras mounted to the mast of the rover to help the mission's team direct the rover. However unlike the previous generation the Curiosity contains an entire inboard laboratory for analyzing the soil and rocks on Mars. NASA engineered the Curiosity to be capable of rolling over obstacles up to 65 centimeters high and traverse up to about 200 meters per day on Martian terrain. Curiosity got its electrical power from a Radioisotope thermoelectric generator.