The Magnetosphere of Jupiter New Perspectives from Galileo and Cassini Fran Bagenal University of...
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Transcript of The Magnetosphere of Jupiter New Perspectives from Galileo and Cassini Fran Bagenal University of...
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
Comparative Magnetospheres
Testing our understanding of Sun-Earth connections through application to other planetary systems
Compressibility
Earth ~ Dipole
Rmp ~ (V2)-1/6
Jupiter
Rmp ~ (V2)-1/3
solar wind V2
solar wind V2
10 RE
100 RJ
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
Cassini flybyDec. 2000
Galileo Orbiter33 orbitsDec. 1995 to Sep. 2003
Voyagers
Pioneers
Ulysses
SolarWind
Magnetopause
Strong magnetic field10 hour rotation periodInternal plasma source
Equatorial plasma diskCorotation with JupiterSlow outward transport
• 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
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
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
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
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
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
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
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
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
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
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
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*
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
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
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.
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
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.
The Io Aurora
Infrared
Ultraviolet
- energetic particles bombard atmosphere- ‘wake’ emission extends halfway around Jupiter
Io
Connerney et al.Clarke et al.
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!
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?
Aurora
Io footprint
Io w
ake
Main Oval
Polar storms- Solar Wind Generated?
Dusk Distortion?
Clarke et al.
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
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.
• 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.
Galileo:The End Game
• Must never hit Earth
100 Rjupiter
Sun
• Must never hit Europa
• Sent into Jupiter Sept. 21st 2003