Galileo Galilei published a book describing four new points of light near Jupiter in March 1610. He had observed these objects with his telescope starting in January that same year.
Simon Marius assigned names to these moons: Io, Europa, Ganymede, and Callisto. Marius found them independently one day after Galileo but did not publish until 1614.
Jupiter hosts dozens of small irregular satellites orbiting far from the main cluster. These bodies likely originated as asteroids captured by the planet's gravity long ago.
By February 2023 the total reached ninety-five after Sheppard announced three additional discoveries from a 2022 survey. Surveys conducted between 2000 and 2004 increased Jupiter's known moon count from seventeen to sixty-three.
Voyager 1 and Voyager 2 probes reached Jupiter in 1979 discovering volcanic activity on Io and water ice on Europa's surface. Pioneer 11 followed a year later taking low resolution images of the four largest moons.