Jupiter and Io photographed by the Voyager 2 probe on 9 July 1979.
Jupiter and Io photographed by the Voyager 2 probe on 9 July 1979.

1979: Voyager 2 made its closest approach to Jupiter on this day, passing within 570,000km of the giant planet’s upper atmosphere.

The twin Voyager spacecraft made numerous discoveries in the Jovian system, including active volcanoes on the moon Io (the first discovered beyond Earth), faint rings encircling the planet and previously unknown moons.

Wikipedia
NASA Voyager homepage

JPL Voyager homepage