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
The "Mars Express" mission of the European Space Agency (ESA) reached Mars in 2003. It carried the "Beagle 2" lander, which was not heard from after being released and was declared lost in February 2004. "Beagle 2" was located in January 2015 by HiRise camera on NASA's "Mars Reconnaissance Orbiter" (MRO) having landed safely but failed to fully deploy its solar panels and antenna. In early 2004, the "Mars Express" Planetary Fourier Spectrometer team announced the orbiter had detected methane in the Martian atmosphere, a potential biosignature. ESA announced in June 2006 the discovery of aurorae on Mars by the "Mars Express".