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.
Yinghuo-1
Yinghuo-1 was a Chinese Mars-exploration space probe, intended to be the first Chinese spacecraft to orbit Mars. It was launched from Baikonur Cosmodrome, Kazakhstan, on 8 November 2011, along with the Russian Fobos-Grunt sample return spacecraft, which was intended to visit Mars' moon Phobos. The 115-kg (250-lb) Yinghuo-1 probe was intended by the CNSA to orbit Mars for about two years, studying the planet's surface, atmosphere, ionosphere and magnetic field. Shortly after launch, Fobos-Grunt was expected to perform two burns to depart Earth orbit bound for Mars. However, these burns did not take place, leaving both probes stranded in orbit. On 17 November 2011, Chinese state media reported that Yinghuo-1 had been declared lost by the CNSA. After a period of orbital decay, Yinghuo-1 and Fobos-Grunt underwent destructive re-entry on 15 January 2012, finally disintegrating over the Pacific Ocean.