In 1610, Galileo Galilei trained his telescope on Jupiter and made the sensational discovery that there were four moons circling that giant planet. This was a startling discovery because at that time everyone believed that all the heavenly bodies, including the sun, circled the earth. The fact that four moons were circling some other planet was a blow to the theory that Earth was the centre of the universe.
Then there was another Galileo studying Jupiter. Launched in 1989, the unmanned spacecraft, Galileo, after a long journey through space was in the orbit around Jupiter. It was the first spacecraft to orbit any of the solar system's outer planets. Galileo discovered the first moon of an asteroid, witnessed the impact of a comet into Jupiter and provided firm evidence of salty oceans on three moons of Jupiter. Galileo also sent back some amazing pictures of the moon Io wherein it captured its volcanoes spewing lava. On 21st Sept 2003, at 19:57 GMT, the unmanned Galileo spacecraft plunged into Jupiter's turbulent atmosphere.