The Voyager 1 mission was part of the NASA grand tour of the solar system. It was launched on September 5th 1977, 16 days after its twin Voyager 2. Their missions were to explore the distant parts of the solar system.
Voyager 1 flew past the gas giants Jupiter and Saturn and sent back incredible images and information that scientists are still studying today. Amongst the many discoveries made by Voyager 1 was that the moon Io had active volcanoes, it was the first object other than the Earth for this to be seen happening. Io was one of the moons that was discovered by Galileo in the winter of 1609/10.
When the probe flew past Saturn and sent back incredible images if the ring system it also examined Titan the largest moon of Saturn. Although it was not possible to see the surface of Titan due to the thick atmosphere there was an indication that there was liquid on the surface. The Cassini mission has indeed conformed that there is liquid on Titan, not water of course but methane.
Voyager 1 then continued on its mission flying to the edge of the solar system and in 2012 scientists confirmed that Voyager 1 was at the very edge of the solar system. It is expected that Voyager 1 will continue working until about 2025.