July 14/15 1965, Mariner transmits the first close-up pictures of Mars back to Earth.
They show ruins of ancient (millions of years old) cities and canals
(note: if anybody actually subsequently makes it to Mars, no Martains are found - the aliens are not indigenous to Mars, and the cities have been stripped of technological artifacts and the language is untranslatable (although nobody knows that so people will try) - although the ruins show they had a highly technological civilization - the only indication of what happened to Mars is a transmitter that seems to be pointed to Phobos, searching Phobos would reveal a bigger transmitter pointed towards Saturn or Saturn's moons).