Juno: Changing Views of Solar Juno: Changing Views of Solar System FormationSystem Formation

Paul G. SteffesProfessor and Associate ChairSchool of ECE, Georgia Institute of Technology

With much assistance from Prof. Fran Bagenal, Univ. of Colorado

JunoJuno

Juno Science Presentation Juno Site Visit – Use or disclosure of any of the information of this package is subject to the restrictions on the cover page.

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Juno Science ObjectivesJuno Science Objectives

OriginDetermine O/H ratio (water abundance) and constrain core mass to decide among alternative theories of origin.

InteriorUnderstand Jupiter's interior structure and dynamical properties by mapping its gravitational and magnetic fields

AtmosphereMap variations in atmospheric composition, temperature, cloud opacity and dynamics to depths greater than 100 bars at all latitudes.

MagnetosphereCharacterize and explore the three-dimensional structure of Jupiter's polar magnetosphere and auroras.

JunoJuno

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Juno Spacecraft & PayloadJuno Spacecraft & Payload

Spacecraft

976kg (dry)

Built around radiation vault

Solar power - 2m x 7.5m arrays, ~300 W

Spacecraft - sun-pointed 3rpm spinner

Operations - simple and repetitive

15 kbps downlink

PayloadGravity Science (JPL)Magnetometer— MAG (GSFC/JPL)Microwave Radiometer— MWR (JPL)Energetic Particle Detector—EPD (APL)Jovian Auroral Distributions Experiment

— JADE (SwRI)Waves (U of Iowa)UV Spectrometer— UVS (SwRI)Visible Camera - JunoCam (Malin)

JunoJuno

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Public Engagement and StudentsPublic Engagement and Students

• “Giant Planet Story is the story of the solar system” Jupiter’s mysteries captivate public interest

• E/PO effort targets unique customer needs and involves students directly in science

• Students analyze the first images of Jupiter’s poles.

No, it's not student-built….

JunoJuno

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Juno Mission DesignJuno Mission Design

Currently in Phase B

Launch: August 2011

5 year cruise

Baseline mission:32 polar orbits Perijove ~5000 km11 day periodSpinnerSolar-powered

Science Objectives:Origin of JupiterInterior StructureAtmosphere Composition & DynamicsPolar Magnetosphere

JunoJuno

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The History of the Solar SystemThe History of the Solar System

Present theories of solar system origin and evolution do not explain how Jupiter was enriched in heavy elements.

This is key to understanding how giant planets form, in our own and other planetary systems.

These heavy elements are the seeds for the Earth and life

Jupiter’s formation – How, when, where, and how long?

JunoJuno

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Galileo Probe ResultsGalileo Probe Results

• Galileo results show similar enrichment in key elements, independent of volatility

• Results imply Jupiter formed colder and/or further out than 5 AU

• Solid material that enriched Jupiter was most abundant solid material in early solar system

Galileo probe abundances challenge planet formation models

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Collapse of the Solar Nebula

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H2O, NH3, CH4 Water, Ammonia, MethaneHydrogen compounds (in Jupiter)

Ignore inert gasesHe, Ne, Ar

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Abundant ice (H2O) condense beyond frost lineSnowballs -> bigger snowballs--> rock-ice planetary coresCores have enough gravity to hold H - most abundant element - > giant planetsSmall amounts of rock & metal-> terrestrial planets

Formation of Jupiter andFormation of Jupiter andOrigin of atmosphereOrigin of atmosphere

Core accretion modelCore accretion model Core from grains of ice, rock, metalCore from grains of ice, rock, metal Core grows to critical mass (poorly understood,~10 MCore grows to critical mass (poorly understood,~10 MEE)) Gravitational collapse: HGravitational collapse: H22, He (most volatile gases) , He (most volatile gases)

capturedcaptured Atmosphere from HAtmosphere from H22, He; and volatiles from core, He; and volatiles from core PlanetesimalsPlanetesimals added throughout the formation (and added throughout the formation (and

afterward) to explain heavy element enrichmentafterward) to explain heavy element enrichmentColdCold icy planetesimals icy planetesimals Clathrate hydrates (stuff bonded in ice)Clathrate hydrates (stuff bonded in ice)

Jupiter clouds Jupiter clouds

Equilibrium(expected)

Hot Spot(Galileo observed)

Galileo Probe Gas Mass Spectrometer

889 nm (0.5 bar)727 nm (3 bar)

756 nm (>3 bar)

Galileo ImagingGierasch, et al; Ingersoll, et al (2000)

lightning

winds

Elemental abundances at JupiterElemental abundances at Jupiter(Galileo Probe Mass Spectrometer, GPMS)(Galileo Probe Mass Spectrometer, GPMS)

30 au

5 au

evaporate + scatter

30K

150K

Interstellar (ISM)30

K

KBOs

30K

Cold planetesimals and heavy element Cold planetesimals and heavy element enrichmentenrichment

Requires TRequires T 30 K to trap N 30 K to trap N22 and Ar and Ar2-4 solar H2O

Origin: clathrate-hydratesOrigin: clathrate-hydratesCold planetesimals from interstellar cloud may Cold planetesimals from interstellar cloud may

not have survived the formation of solar nebula not have survived the formation of solar nebula (high T)(high T)

Clathrate hydrates trap volatiles containing Clathrate hydrates trap volatiles containing heavy elements in the cooling, feeding zone heavy elements in the cooling, feeding zone of Jupiterof Jupiter

Predicts Predicts 99 solar H solar H22OO, with 100% efficiency , with 100% efficiency of trapping in clathrates (Gautier of trapping in clathrates (Gautier et alet al., 2001) ., 2001)

What is missing?What is missing?

abundance in “well-mixed” atmosphereabundance in “well-mixed” atmosphere

HH22OO is presumably the original carrier of is presumably the original carrier of heavy elements to Jupiter.heavy elements to Jupiter.

Help is on the way! JunoHelp is on the way! Juno

WaterWater

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What water tells us!What water tells us!

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Jupiter’s AtmosphereJupiter’s Atmosphere

Water is likely carrier of heavy elements to the solar system

Galileo was unable to determine global water abundance

The source of the belt-zone structure unknown

Jupiter’s atmosphere can tell us where and when?

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Microwave RadiometryMicrowave Radiometry

Radiometry sounds atmosphere to 1000 bar depth

Determines water and ammonia global abundances

6 wavelengths between 1.3 and 50 cm

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Microwave Radiometry 2Microwave Radiometry 2

• Global coverage ensures accurate measurement

• Observations investigate roots of belt-zone structure

• Builds on Earth (TOPEX, MISR, JASON) and Astrophysics (COBE) missions

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Microwave Radiometry from 0.5 to >100 Bars Microwave Radiometry from 0.5 to >100 Bars

Short wave channels sample NH3 cloud

Long wave channels sample H2O cloud and below

Gives 3D coverage - latitude, emission angle, wavelength

Water is crucial for origin of solar system and meteorology

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How Did We Get this Up Here?How Did We Get this Up Here?How Did We Get this Up Here?How Did We Get this Up Here?

•544 kg (1200 lbs)

•+ •=•726 kg (1600 lbs)

•136 kg (300 lbs)

•Measurement SystemSensitivity StudySummary

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How Does it all fit together?How Does it all fit together?How Does it all fit together?How Does it all fit together?

•Measurement SystemSensitivity StudySummary

JunoJunoLet's go!