Why the Juno mission is important to space science, from Kenneth Chang at the New York Times:

Jupiter, most likely the first planet formed after the sun, is believed to hold the keys to understanding the origins of our solar system. How much water it contains and the possible presence of a rocky core could reveal where in the solar system Jupiter was created and provide clues to the early days of other planets.

Juno’s instruments are designed to precisely measure the magnetic and gravitational fields of Jupiter and the glow of microwaves emanating from within. That, for instance, will give hints about storm systems like the visible Great Red Spot, which has persisted for centuries, although it has been shrinking.

The New York Times also put together some terrific graphics and video on the mission.