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.
Soviet space program
The Soviet space program (Russian: Космическая программа СССР, "Kosmicheskaya programma SSSR") comprised several of the rocket and space exploration programs conducted by the Soviet Union (USSR) from the 1930s until its collapse in 1991. Over its sixty-year history, this primarily classified military program was responsible for a number of pioneering accomplishments in space flight, including the first intercontinental ballistic missile (R-7), first satellite (Sputnik 1), first animal in Earth orbit (the dog Laika on Sputnik 2), first human in space and Earth orbit (cosmonaut Yuri Gagarin on Vostok 1), first woman in space and Earth orbit (cosmonaut Valentina Tereshkova on Vostok 6), first spacewalk (cosmonaut Alexey Leonov on Voskhod 2), first Moon impact ("Luna 2"), first image of the far side of the moon ("Luna 3") and unmanned lunar soft landing ("Luna 9"), first space rover ("Lunokhod 1"), first sample of lunar soil automatically extracted and brought to Earth ("Luna 16"), and first space station (Salyut 1). Further notable records included the first interplanetary probes: Venera 1 and Mars 1 to fly by Venus and Mars, respectively, Venera 3 and Mars 2 to impact the respective planet surface, and Venera 7 and Mars 3 to make soft landings on these planets.