Juno is unique in that it employed solar panels as its energy source instead of the nuclear (RTG) power system used by previous missions this far out in the solar system. Jupiter is at the limit of distance from the Sun in to what can be achieved from solar power. To make solar power practical, Juno carries relatively enormous solar panels.
Juno's mission was to measure Jupiter's composition, gravitation and magnetic fields and in particular the Jovian polar magnetosphere and aurorae.
Juno has also explored some of the moons of Jupiter, including Ganymede, Europa and Io.
The orbits of Juno were arranged to minimise the radiation dose from the giant radiation belts of Jupiter.
