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.
CubeSat
The May 2018 launch of the "InSight" stationary Mars lander included two CubeSats to flyby Mars to provide additional relay communications from "InSight" to Earth during entry and landing. This is the first flight of CubeSats in deep space. The mission CubeSat technology is called Mars Cube One (MarCO), each one is a six-unit CubeSat, 14.4 inches (36.6 centimeters) by 9.5 inches (24.3 centimeters) by 4.6 inches (11.8 centimeters). MarCo is an experiment, but not necessary for the "InSight" mission, to add relay communications to space missions in important time durations, in this case from the time of "InSight" atmospheric entry to its landing.