2. Juno is the sixth craft to visit Jupiter, and the first new visitor in decades
The exploration of Jupiter began in 1973 when Pioneer 10 flew by the gas giant. Pioneer 11 flew the next year. Pioneer 10 was meant to study Jupiter's radiation for future missions. In the process of this study, the craft was damaged (though not destroyed) by the unexpectedly harsh radiation.
A few years later, Voyagers 1 and 2 performed flybys in 1979, the first in March and the next in July. Those crafts took breathtaking photos of the systems and gave the first hints that Jupiter's moon, Europa, may harbor an ocean.
NASA didn't send an orbiter to Jupiter until Galileo was launched in 1989, taking a more leisurely pace to Jupiter than any previous visitors in order to enable a gravitational capture. The probe arrived in 1995 and studied the planet and its moons for eight years before plunging to its death into Jupiter in 2003 to ensure none of the moons became contaminated, as Europa and Ganymede (and to a lesser extent, Callisto) are believed to have oceans and the possibility of life.
Juno, originally launched in 2011, is the second orbiter and will concentrate mostly on studying Jupiter itself.