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.
Exploration of Mars
In August 2012, NASA selected "InSight", a $425 million lander mission with a heat flow probe and seismometer, to determine the deep interior structure of Mars. Two flyby CubeSats called MarCO were launched with "InSight" on 5 May 2018 to provide real-time telemetry during the entry and landing of "InSight". The CubeSats separated from the Atlas V booster 1.5 hours after launch and traveled their own trajectories to Mars. "InSight" landed successfully on Mars on 26 November 2018.
Other future mission concepts include polar probes, Martian aircraft and a network of small meteorological stations. Longterm areas of study may include Martian lava tubes, resource utilization, and electronic charge carriers in rocks. Micromissions are another possibility, such as piggybacking a small spacecraft on an Ariane 5 rocket and using a lunar gravity assist to get to Mars.