Juno: Changing Views of Solar
System Formation
Paul G. Steffes
Professor and Associate Chair
School of ECE, Georgia Institute of
Technology
With much assistance from Prof. Fran
Bagenal, Univ. of Colorado
Juno Science Objectives
Juno
Origin
Determine O/H ratio (water abundance) and
constrain core mass to decide among alternative
theories of origin.
Interior
Understand Jupiter's interior structure and
dynamical properties 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.
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.
2
Juno Spacecraft & Payload
Juno
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
Payload
Gravity 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)
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.
3
Juno
Public 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….
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.
4
Juno Mission Design
Juno
Currently in Phase B
Launch: August 2011
5 year cruise
Baseline mission:
32 polar orbits
Perijove ~5000 km
11 day period
Spinner
Solar-powered
Science Objectives:
Origin of Jupiter
Interior Structure
Atmosphere Composition & Dynamics
Polar Magnetosphere
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.
5
The History of the Solar System
Juno
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?
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.
6
Galileo Probe Results
Juno
• 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
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.
7
Collapse of the Solar Nebula
8
H2O, NH3, CH4
Water, Ammonia, Methane
Hydrogen compounds (in Jupiter)
Ignore inert gases
He, Ne, Ar
9
Abundant ice (H2O) condense beyond frost line
Snowballs -> bigger snowballs--> rock-ice planetary cores
Cores have enough gravity to hold H - most abundant
element - > giant planets
Small amounts of rock & metal-> terrestrial planets 10
Formation of Jupiter and
Origin of atmosphere
Core accretion model





Core from grains of ice, rock, metal
Core grows to critical mass (poorly understood,~10
ME)
Gravitational collapse: H2, He (most volatile gases)
captured
Atmosphere from H2, He; and volatiles from core
Planetesimals added throughout the formation (and
afterward) to explain heavy element enrichment
 Cold icy planetesimals

Clathrate hydrates (stuff bonded in ice)
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)
lightning
winds
Galileo Imaging
Gierasch, et al; Ingersoll, et al (2000)
Elemental abundances at Jupiter
(Galileo Probe Mass Spectrometer, GPMS)
Cold planetesimals and heavy element
enrichment
Requires T 30 K to trap N2 and Ar
2-4 solar H2O
Interstellar (ISM)
30K
evaporate
+ scatter
KBOs
30K
150K
5 au
30K
30 au
Origin: clathrate-hydrates
Cold planetesimals from interstellar cloud may
not have survived the formation of solar nebula
(high T)

Clathrate hydrates trap volatiles containing
heavy elements in the cooling, feeding zone
of Jupiter

Predicts 9 solar H2O, with 100% efficiency
of trapping in clathrates (Gautier et al.,
2001)
What is missing?
Water
abundance in “well-mixed” atmosphere
H2O is presumably the original carrier of
heavy elements to Jupiter.
Help is on the way! Juno
What water tells us!
19
Jupiter’s Atmosphere
Juno
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?
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.
20
Microwave Radiometry
Juno
Radiometry sounds
atmosphere to 1000 bar
depth
Determines water and
ammonia global
abundances
6 wavelengths between
1.3 and 50 cm
Juno Science Presentation
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21
Microwave Radiometry 2
Juno
• Global coverage
ensures accurate
measurement
• Observations
investigate roots of
belt-zone structure
• Builds on Earth
(TOPEX, MISR, JASON)
and Astrophysics
(COBE) missions
Juno Science Presentation
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22
Juno
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
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.
23
Juno
•Measurement System
Sensitivity Study
Summary
How Did We Get this Up Here?
•136 kg (300 lbs)
•726 kg (1600 lbs)
•544 kg (1200 lbs)
•+
•=
Juno
•Measurement System
Sensitivity Study
Summary
How Does it all fit together?
Juno
Let's go!