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The Magnetosphere of Jupiter
New Perspectives from Galileo and Cassini
Fran BagenalUniversity of Colorado
TitleThe Magnetosphere
of Jupiter
New Perspectives from Galileo and Cassini
Fran BagenalUniversity of Colorado
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Comparative Magnetospheres
Testing our understanding of Sun-Earth connections through application to other planetary systems
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Compressibility
Earth ~ Dipole
Rmp ~ (V2)-1/6
Jupiter
Rmp ~ (V2)-1/3
solar wind V2
solar wind V2
10 RE
100 RJ
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compress 2Earth ~ Dipole
Jupiter
solar wind V2
solar wind V2
Rmp -> 0.5 Rmp
Rmp -> 0.7 Rmp
Factor ~10 variations in solar wind pressure at 5 AU -> observed 100-50 Rj size of dayside magnetosphere
7 RE
50 RJ
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~10
<<1
= nkT B2 /8
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IoGanymede Europa
Callisto
1 ton / sec
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Galileo Mission
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Galileo Spacecraft
spins 3 rpm
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Cassini flybyDec. 2000
Galileo Orbiter33 orbitsDec. 1995 to Sep. 2003
Voyagers
Pioneers
Ulysses
SolarWind
Magnetopause
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SOLAR WINDRotation + Outflow
SolarWind
EARTHSolar Wind Driven Convection
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Strong magnetic field10 hour rotation periodInternal plasma source
Equatorial plasma diskCorotation with JupiterSlow outward transport
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• As plasma from Io flows outwards its rotation decreases (conservation of angular momentum)
• Sub-corotating plasma pulls back the magnetic field
• Curl B -> radial current
• J x B force enforces rotation
Jupiter - Momentum Coupling
Field-aligned currents couple magnetosphere
to Jupiter’s rotation
Khurana 2001
Cowley & Bunce 2001
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Disks, B, Stellar Rotation, & JetsDisks, B, Stellar Rotation, & Jets John Bally
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Global Structure & Dynamics• Galileo - Survey of magnetic field in the equator -> structure and current systems
Earth-like
Jupiter-like
Rotation modifies structure at Jupiter
Khurana 2001
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Global Structure & Dynamics
Ogino et al.
Krupp et al.
EPD data
Flow Pattern in the Equator
• In situ plasma measurements
• Rotation dominates to >140 RJ
• Local time asymmetry
• Observed flow pattern consistent with MHD simulations but ~1.5 times stronger.
• Abrupt bursts
Bursts
Super-rotation
MHD simulation
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Global Dynamics - Outstanding Questions
•What happens in the magnetotail?
• What happens above the equator?
• How is angular momentum transferred from Jupiter to the magnetosphere?
• What are the roles of Io’s volcanism vs. solar wind in magnetospheric variability?
•What triggers disruptions?
Vasyliunas 1983
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Ganymede Europa & Callisto
Satellites in the Magnetosphere
• Dynamo in iron core• Magnetosphere within a magnetosphere
• Radiolysis of surface
• Currents induced by changing field indicate liquid water layer
GalileoNIMSIR image
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Io
Amirani
300 km
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After quantities of lava are removed from below, the crust cracks and tilts, making tall, blocky mountains.
Tvashtar
Hiiaka Patera
50 km
11 km high
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Io’s Volcanoes& Geysers
InfraRed
Pilan 5 months apart
Prometheus
Pilan Plume
Pele
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Galileo - Nightside of Io - Visible
Glowing Lava
Plume Gas & Dust + Aurora
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After Spencer & Schneider 1996
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Io-plasma interaction: HST data vs model
Hubble Space Telescope image of O+ emission - Roessler et al. 1997
MHD model of Io interaction - prediction of O+ emission excited by electron impact - Linker & McGrath 1998
Jupiter
Flow
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Io Plasma Torus
Source: Extended clouds O, S, SO, SO2, S2..? ~1 ton/s ~3 x 1028 ions/s n/n~2% per rotation
Warm Torus: 90% of plasma Ne~2000 cm-3 O+ S++
Ti~100eV Te~5eV UV power ~ 2 x 1012 W
Cold Torus: Ne~1000 cm-3 S+
Ti~Te~1 eV Local Io Source? ~20%?
UV
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Io Plasma Torus (Schneider & Trauger)
S+
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Cassini UVIS - PI Larry Esposito, University of Colorado• Movie - 45 days as Cassini approached Jupiter• Integration over multiple lines in the EUV
= direction of dipole tiltE W brighter
Io Plasma Torus
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Wavelength
Image of Torus in O+ EmissionS++ Emission Jupiter’s Aurora
110°
200°
290°
Steffl
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How do composition, temperatures and UV power vary?
Cassini UVIS
600A
1900A
Steffl
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How do composition, temperatures and UV power vary?T
era
Wat
ts S+++
O+O+
S++
S+++
S+
Oct Jan Apr 2000 2001
1 2 3Steffl
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Models of Torus Chemistry
Neutral Cloud Theory:Source = atomic O, SIonization, Charge Exchange, RecombinationRadiative CoolingIon-Electron coupling - Coulomb collisions
Electron heating: Necessary to provide UV emitted powerUsually specified as Fhot=Nehot/Necold and
Thot
Barbosa, Shemansky, Smith&Strobel, Schreier et al., Lichtenberg, Delamere
Atomic data issues
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Energetic Particle Recycling
After Thorne (1983)
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3 - Energetic Particle RecyclingEnergetic Particle Recycling
After Thorne (1983)
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Energetic Particle Recycling
Krimigis et al.
• Energetic Neutral Atoms - charge exchange
S+ + O -> O+ +
• 50-80 KeV/nucleon
• Few % of torus’ 1 ton/sec
• Re-ionization of fast neutral wind • Cassini/MIMI saw pick-up ions > 2 AU from Jupiter
• H+, He++, He+, O+, S+ Molecules?!
Cassini MIMI
S*
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Krimigis et al.
Energetic Particle Recycling
Mendillo et al.
Extended Fast/Energetic Neutral Wind
• Sodium - ground-based telescopic observations of scattered sunlight - cold neutral wind from charge-exchange of torus ions
•MIMI observations of hot neutral sulfur and oxygen (molecules?) from charge-exchange of radiation belt particles >2 AU away
Sodium
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Jupiter Radio Emission Discovered in 1955
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Early Discoveries
Io’s Orbital Period = 42 hours
Jupiter’s Spin Period = 10 hoursJupiter’s Radio Emission Controlled by - Location of Io - Magnetic Longitude
Io Phase
Longitude
BA A
B
AB
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Early Explanations
Dulk (1965)
Goldreich & Lyndon-Bell (1969)
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1979 Voyager flyby - The Io Alfven Wave
Looking From Side
Looking Upstream
Io’s motion through Jupiter’s magnetic field induces strong electrical currents which propagate as MHD waves along the field lines towards Jupiter.
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Voyager Radio Discoveries
• Repeated patterns of arcs in frequency-time spectrographs
• Indicates systematic beaming pattern, controlled by the geometry of Jupiter’s magnetic field.
Carr et al. 1983
Warwick et al. 1979Voyager PRA
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Alfven Wave Theory
Gurnett & Geortz 1982
• Io generates Alfven waves
• Pattern of reflected waves carried downstream by corotating magnetospheric plasma
• Each Alfven wave excites an arc of radio emission.
• Nice idea—but probably little wave power reaches high latitudes.
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Galileo Io Flyby - 1995
Flow
Magnetic field
Electron Beams
Galileo
Fresh hot ions
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The Io Aurora
Infrared
Ultraviolet
- energetic particles bombard atmosphere- ‘wake’ emission extends halfway around Jupiter
Io
Connerney et al.Clarke et al.
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Delamere et al. 2003Saur et al. 2002
Io Plasma-Atmosphere Interaction
• Electrodynamics: Induction and Pick-up currents deflect flow • Heating, ionization and charge-exchange in atmosphere• Cooling, deceleration of upstream plasma• Acceleration of downstream plasma• Messy!
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Delamere et al. 2003
Phase II: Pick-up of New Plasma in Io’s Wake
• Coupling to torus plasma
• Alfven travel-time to “edge” of torus
• Acceleration to few% of corotation
• 2-D MHD in non-uniform background plasma
What happens between the torus and Jupiter where the density is very low?
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Ergun et al.
Lessons from FAST at Earth
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Ergun et al.
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Su et al. 2003
EARTH
JUPITER
1-D Vlasov code
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Aurora
Io footprint
Io w
ake
Main Oval
Polar storms- Solar Wind Generated?
Dusk Distortion?
Clarke et al.
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AuroraThe aurora is the signature of Jupiter’s attempt to spin up its magnetosphere
Clarke et al.
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TORUS POWER
How does UV power of the torus and aurora vary?
TORUS POWER
AURORAL POWER
Oct Jan Apr 2000 2001
Ter
a W
atts
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The Jupiter-Io system is a complex interconnected system.
The Jupiter-Io System: The Big Picture
Although the phenomena shown here have been well studied individually, the cause-and-effect relationships between them have not been established.
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SMEX mission
Earth-orbiting UV telescope to observe Io, the torus and Jovian aurora
Trying Again!
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JunoJunoJupiter Jupiter Polar Polar
OrbiterOrbiter
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• Moving beyond initial exploration to address focused questions
• Challenging understanding of fundamental magnetospheric processes by exploring different parameter regimes
• Reconnection
• Cross-field diffusion
• Alfvenic acceleration
• Parallel electric fields
• Cross-scale coupling
• Momentum transfer
Jupiter Polar Mission
By testing our understanding of concepts developed at Earth through exploring the magnetosphere of Jupiter we open our
eyes and see our own magnetosphere in a different light.
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Galileo:The End Game
• Must never hit Earth
100 Rjupiter
Sun
• Must never hit Europa
• Sent into Jupiter Sept. 21st 2003
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Let’s Keep Exploring!Let’s Keep Exploring!
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