|Artist's Impression of Juno circling Jupiter.|
Juno's aim is to study Jupiter's atmosphere and its gravitational and magnetic fields. The hope is that this data will give clues to Jupiter's origins. For example, if Juno detects a high concentration of water in Jupiter's atmosphere, that would suggest that Jupiter might have formed further out in the Solar System and gradually drifted to its current position.
Juno's year-long study will end in dramatic fashion, with the probe plunging deep into the depths of Jupiter and being destroyed.
See the Juno mission page from NASA: http://www.nasa.gov/mission_pages/juno/main/index.html