Here on Earth, people were thrilled to get their first look at the surface of neighbouring planet Mars this week in 1965, all thanks to the Mariner 4.
The American spacecraft, launched in November 1964, performed the first successful fly-by of the planet, and sent back the first pictures of its surface.
The photographs were carried by weak but steady radio signals bit by bit over 215 million km in space - the process was so sensitive that it took eight hours and 35 minutes to transmit just one shot.
The spacecraft also transmitted other important information, such as evidence that Mars had virtually no magnetic field - which meant that it was unlikely to have a molten core like Earth's.
The first few pictures were taken at a distance of 16,898km from the planet's surface, but subsequent images were shot from only half that distance.
The head of the Mariner 4 project, Mr Dan Schneiderman, said: "We never, at any time, ever dreamt we would get anywhere close enough to look for life."
He added that no signs of plant or animal life had been spotted in the images sent back to Earth.
Subsequent study of the pictures suggested strongly that Mars had no rivers or oceans, and that it was too dry to support any kind of multi-cellular life.