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.
Landing
Sometimes, a safe landing is accomplished by using multiple forms of lift, thrust ("propulsive landing") and dampening systems. Both the Surveyor unmanned lunar probe craft, and the Apollo Lunar Module used a rocket deceleration system and landing gear to soft-land on the moon. Several Soviet rockets including the Soyuz spacecraft have used parachutes and airbag landing systems to dampen the landing on earth. In November 2015, Blue Origin's New Shepard became the first rocket to cross the van Karman line and land vertically back on Earth. In December 2015, SpaceX's Falcon 9 became the first launch vehicle on an orbital trajectory to successfully vertically-land and recover its first stage, although the landed first stage was on a sub-orbital trajectory.