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.
ExoMars
The Entry, Descent and Landing Demonstrator Module (EDM) called "Schiaparelli", was intended to provide the European Space Agency (ESA) and Russia's Roscosmos with the technology for landing on the surface of Mars. It was launched together with the ExoMars Trace Gas Orbiter (TGO) on 14 March 2016 and was scheduled to land softly on 19 October 2016. No signal indicating a successful landing was received, and on 21 October 2016 NASA released a Mars Reconnaissance Orbiter showing what appears to be the lander crash site. The lander was equipped with a non-rechargeable electric battery with enough power for four sols. The soft landing should have taken place on Meridiani Planum during the dust storm season, which would have provided a unique chance to characterise a dust-loaded atmosphere during entry and descent, and to conduct surface measurements associated with a dust-rich environment.