What Motivated the Juno Mission?

The results from the last dedicated mission to Jupiter; the Galileo Orbiter and Probe, raised many new questions about the formation, origins and evolution of the solar system. The Probe results showed that the planet was depleted in water at the location it sampled. Water is thought to be the carrier for the heavy elements into the outer solar system. The question remains as to how a gas giant such as Jupiter acquired the heavy elements. Because such heavy elements are necessary for the formation of terrestrial planets such as Earth, and for life itself, the answer to the remaining questions regarding Jupiter's formation will provide key new knowledge about our own beginnings.


The existence of a solid core distinguishes between the two main competing theories of Jupiter’s formation. One theory suggests that Jupiter formed from the accretion of material from its nearby neighborhood, while the other leading theory proposes formation by the collapse of a condensing cloud of dust and gases under gravity. Each theory leads to a very different evolutionary path for a planet such as Jupiter. From its external observable features, Jupiter provides us with clues to its interior, its zonal winds, internal composition, the structure of its magnetic field that is generated in the deep interior by a dynamo, its magnetosphere and the aurora. The Juno mission will obtain precise measurements of Juptier's gravity, its magnetic field and internal composition from a highly elliptical orbit and answer the critical questions regarding Jupiter's formation of, "How,? Where?, When?, and How long?" Answers to these questions will reveal key clues to the origins of our solar system, and even life itself. The Juno mission will make significant advances in our understanding of these fundamental questions by:

  • Precise monitoring of the Juno spacecraft around Jupiter provides measurements of the gravity field of Jupiter. Unlike Galileo, Juno is in a polar orbit around Jupiter, which enables sampling of the global gravity field. The gravity field is determined by the distribution of mass in the interior and thus reveals information about Jupiter's core and the deep structure.
  • Precise mapping of the magnetic field measurements by a sensitive magnetometer will reveal fundamental dynamical processes. Similar to the gravity field, Juno's polar orbit will enable complete mapping of the asymmetries and detailed structure of Jupiter's magnetic field which influences its auroral processes and magnetosphere.
  • Probing the atmosphere below the clouds with its microwave radiometer to a depth of ~ 100 bar pressure to determine the water and ammonia abundances over the planet using six different radio frequencies that probe to different depths. The revealed thermal structure and composition along meridians will inform us about Jupiter's intriguing belt-zone structure as evidenced by colorful bands at the cloud level.
  • Juno's orbit carries it directly through the auroral field lines in the polar magnetosphere. The particles and fields instrument will measure the impinging charged particles into the atmosphere that generate the complex auroral patterns while the measurments by the plasma/radio waves instrument will tell us how the particles are accelerated in the Jupiter's magnetosphere.
  • UV images from the imaging spectrometer will provide close up images of the dynamic aurora.