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Unlocking the Giant Planet Story www.nasa.gov

The Galileo mission dropped a probe into Jupiter’s atmosphere in 1995 and showed us our planetary formation theories were wrong!
The probe results showed Jupiter’s atmosphere was enriched with heavy elements
(heavier than helium, that is), compared to the Sun. The amount of enrichment was similar for everything measured, even compounds that should easily melt or evaporate.
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This meant that Jupiter might have formed farther from the Sun that its present orbit, where it was much colder and easily melted materials could exist in the same amounts as materials that form at higher temperatures. Or it could mean that the easily melted material was trapped inside ice that was able to form near Jupiter’s present position.
In either case, understanding Jupiter’s formation can tell us a lot about what the early solar system was like.
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• Over what period in the early solar system did gas giants form, and how did birth of Jupiter and its gas-giant sibling, Saturn differ from the “ice giants” Uranus and Neptune?
• What is the history of water and other volatile compounds across our solar system?
• How do processes that shape the present character of planetary bodies operate and interact?
• We see a lot of giant planets around other stars. What does our solar system tell us about development and evolution of extrasolar planetary systems, and vice versa?
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Solar System Exploration Decadal Survey 2003 set some principal objectives for a future Jupiter mission:
Determine if Jupiter has a central core to constrain models of its formation
Determine the planetary water abundance
Determine if the winds persist into Jupiter’s interior or are confined to the weather layer
Assess the structure of Jupiter’s magnetic field to learn how the internal dynamo works
Measure the polar magnetosphere to understand its rotation and relation to the aurora
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Origin
Determine the abundance of water and place an upper limit on the mass of Jupiter’s solid core to decide which theory of the planet’s origin is correct
Interior
Understand Jupiter's interior structure and how material moves deep within the planet by mapping its gravitational and magnetic fields
Atmosphere
Map variations in atmospheric composition, temperature, cloud opacity and dynamics to depths greater than 100 bars at all latitudes
Magnetosphere
Characterize and explore the three-dimensional structure of Jupiter's polar magnetosphere and auroras.
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Existence & size of the planet’s solid core helps discriminate among giant planet formation theories – which one is correct or are new explanations needed?
Whether the planet accreted onto a solid core or resulted from gravitational collapse of the solar nebula leads to different histories for Jupiter
Structure of Jupiter tells us how interior rotates
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Precise measurements of spacecraft motion measure gravity field
Gravity field tells us about how the mass is distributed inside the planet
Tides caused by the moons provide further clues about the planet’s interior structure
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Microwave antennas (radio waves) probe deep into the cloud layers – just the very top of the atmosphere, where weather occurs
Magnetic fields probe into the region where the magnetic field is generated – the metallic hydrogen layer
Gravity fields probe into the central core region
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Microwave Radiometer Antennas sense the deep atmosphere
How deep are the roots of
Jupiter’s storms and other cloud features? We don’t know!
They could be connected to deep movements of the interior, or they could be shallow surface features.
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Precise magnetic field measurements unveil fundamental processes that generate the planet’s powerful magnetic field
Juno’s polar orbit provides complete mapping of planet’s asymmetric and highly structured field
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Electrically charged atomic particles crash into the atmosphere along magnetic field lines.
When these particles crash into the atmosphere they create light (the auroral or northern lights)
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Juno passes directly through auroral field lines
Measures particles precipitating into atmosphere creating aurora
Plasma/radio waves reveal processes responsible for particle acceleration
UV, IR images provides context for in-situ observations
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Suite of instruments will collect data on:
–Jupiter’s Gravity Field
–Jupiter’s Magnetic Field
–Deep Atmospheric
–Aurora/Magnetosphere
Gravity Science system (JPL)
Magnetometer — MAG (GSFC)
Microwave Radiometer — MWR (JPL)
Energetic Particle Detector — JEDI (APL)
Jovian Auroral Distributions Experiment — JADE (SwRI)
Radio & Plasma Wave Detector (U of Iowa)
Ultraviolet Spectrometer — UVS (SwRI)
Infrared Camera – JIRAM (Italian Space Agency)
Visible Camera - JunoCam (Malin)
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Juno’s orbit avoids the worst of Jupiter’s dangerous radiation belts, but the orbit shifts into increasingly intense radiation zones over the course of the mission.
Fortunately Juno completes its mission in about a year, before radiation can destroy its sensitive electronics.

Images of Solar System Formation
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