Introduction

Jupiter, one of the brightest objects in the sky, was named after the mightiest of the Roman gods because of its dominance. More massive than the other planets combined, Jupiter with its rings and satellites has been likened to a “miniature Solar System.” More than 400 years of telescopic observations and, more importantly, flights of the Pioneer, Voyager, Galileo, Cassini, and New Horizons spacecraft have yielded images and other data for the Jovian system that are among the most spectacular in the Solar System.

Exploration

Scientific exploration of the Jupiter system was begun in 1610 by Galileo Galilei. He had been waiting many days for the night-time skies to clear so that he could try out a new, technically advanced instrument. But it was January in the town of Padua in northern Italy where he worked and winter skies were frequently cloudy. Then, on January 7, a break in the weather brought a sparkling clear night, and Galileo was able to use the new invention to discover a fascinating set of worlds. These discoveries not only brought Galileo much acclaim but also led to a series of military contracts to put the invention to other uses. The invention was the telescope, and, although Galileo did not invent it, he was probably the first to use the telescope to study the heavens, leading to his discovery of the four large moons of Jupiter.