Thanks to: Margaret Kivelson
David BrainSteve Bartlett
Fran BagenalUniversity of
Colorado
Ganymede, MercuryGanymede, Mercury- what a magnetic field says about a core- magnetosphere within a magnetosphere
MarsMars- surface magnetization- atmospheric loss
Europa, CallistoEuropa, Callisto- radiation of surfaces- induction in conducting shell -> water
IoIo- volcanism, patchy atmosphere- aurora
Comets + PlutoComets + Pluto
The Space Environment of Planets
Planetary DynamosPlanetary Dynamos
Volume of electrically conducting fluid ... which is convecting ... and rotating
All planetary objects probably have enough rotation - the presence (or not) of a global magnetic field tells us about
21
21 and
Scales
Earth
• LARGE• Rotating with planet• Jupiter + Saturn:
• dipole with small tilt • dynamo in metallic hydrogen
• Uranus + Neptune:• multipole, large tilt• dynamo in water/ammonia/methane layer
Magnetospheres of the Giant Planets
Mercury - Magnetic field detected by Mariner 10 in 1974
Mercury & GanymedeMercury & Ganymede
Diameter of Earth
SolarWind
Ganymede - Magnetic field detected by Galileo in 1996
Bsurface ~ 1/100 Earth
Mercury & GanymedeMercury & Ganymede
What drives convection in these small bodies?
Liquid Fe + SCore
Liquid Iron Core
Iron Core-Liquid?
““The test of a good theorist The test of a good theorist is the ability to explain any is the ability to explain any outcome, even when the outcome, even when the data are wrong” data are wrong”
- David Stevenson- David Stevenson
Ganymede: A Magnetosphere Ganymede: A Magnetosphere within a Magnetospherewithin a Magnetosphere
Torrence Johnson
Ganymede’s mini-magnetosphere controls Ganymede’s mini-magnetosphere controls the motion of energetic charged particlesthe motion of energetic charged particles
Galileo
Ambient magnetic field
Closed Ganymede magnetic field lines
Open-closed boundaryOpen-closed boundary
Kivelson et al. 1996
Magnetic field Magnetic field coupling coupling Ganymede to Ganymede to JupiterJupiter
Aurora on Ganymede
Khurana & Pappalardo
North Polar Cap
South Polar Cap
HST observations of oxygen emissions - McGrath
Trailing Side = Upstream
Leading Side = Downstream
EnergeticParticles
Mars Global SurveyorMagnetometer - PI: M. Acuna
No core dynamo today
Magnetization of surface rocks
Magnetization only of old, cratered terrain -> Dynamo ceased ~3.5 billion years ago
Ionosphere
Atmospheric Loss Processes
NeutralNeutralIonIon
Bulk removal“stripping”
Ion pickup
SputteringPhotochemical loss
Crustal magnetic sources affect these processes:
shielding atmosphere from SW field topology open field lines
MGS Measurements - Implications
for Mars’ Atmosphere
• Ancient dynamo-> early protection for atmosphere
• Strong crustal magnetization-> affect atmospheric loss after dynamo turn-off
Solar Wind Interaction Boundary
Pressure Balance: obstacle
to the solar wind
PSolar Wind =
P (magnetic)crust
+ P (thermal)ionosphere
David Brain
Mars’Interaction Boundary Response to the Solar Wind
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Field Topology
David Brain
Solar wind and magnetic field impinging on Mars’ complex magnetic field
Close-up of strong anomaly region
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Changing Topology of Mars’ Magnetic Field
Over a Strong Magnetic Region
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Mars Aeronomy Mission
Upper atmosphere Ionosphere Magnetic Field Pick-Up Ions Solar Wind
Galileo Galileo MissionMission
The Galilean SatellitesThe Galilean Satellites
The Magnetosphere of Jupiter
New Perspectives from Galileo and Cassini
Fran BagenalUniversity of Colorado
Title
EuropaEuropa
CallistoCallisto
GanymedeGanymede
IoIo
Think of a moon embedded in a plasma which overtakes the moon in the direction of its orbital motion.
THEN - the atmosphere is ionized & stripped away by the magnetosphere
Europa & Callisto Radiolysis -
Galileo Near InfraRed Mapping Spectrometer image of Europa showing distribution of hydrated sulfur compounds
Bombardment of surface ices and minerals by energetic particles from the magnetosphere
- changes chemistry- alters grain size- embedded heavy ions- sputtering
““Because of the magnetosphere, the Because of the magnetosphere, the Galilean satellites have all lost the Galilean satellites have all lost the equivalent of a Titan (or Earth) equivalent of a Titan (or Earth) atmosphere over the past billion atmosphere over the past billion years” years”
- Bob Johnson- Bob Johnson
Induced Currents -> Oceans• A moon sees a changing magnetic field as Jupiter’s tilted magnetosphere rotates
• Electrical currents induced in a electrically conducting layer produce a magnetic perturbation - observed by Galileo • Observed magnetic field
perturbations imply water layers in Callisto and Europa, possibly Ganymede
• Depth and thickness of water layer not uniquely determined
Io
Amirani
300 km
Io’s Volcanoes& Geysers
Infrared glow
Pilan 5 months apart
Prometheus
Pilan Plume
PelePele
Glowing Lava
Plume Gas & Dust + Aurora
Io at night - Io at night - GalileoGalileo visible image visible image
After Spencer & Schneider 1996
Plasma collides with atmosphere on the flanks
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 Io Plasma Torus - ground-based telescope- ground-based telescope
S+
Schneider & Trauger
Source of plasma = 1 ton of sulfur and oxygen ions per second
Cassini UltraViolet Imaging SpectrometerLarry Esposito, University of Colorado
• UV images of the toroidal cloud of ions at Io’s orbit, • The S+ , O+ ions are trapped by Jupiter’s magnetic field. • Jupiter is dark at UV wavelengths.
= direction of dipole tiltE W brighter
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Dulk (1965)
Early Radio Observations & Explanations
Goldreich & Lyndon-Bell (1969)
Radio Beam
The Io Aurora
Infrared
Ultraviolet
- energetic particles bombard atmosphere- ‘wake’ emission extends half way around Jupiter
Io Footprint Io Footprint AuroraAurora
Aurora
The aurora is the The aurora is the signature of signature of Jupiter’s attempt Jupiter’s attempt to spin up its to spin up its magnetospheremagnetosphere
Clarke et al.
Main Oval
Io footprint + wake G E
Jupiter’s Extended Corona
Charge exchange of energetic charged particles with neutral clouds around orbits of Io and Europa -> escaping Energetic Neutral Atoms
=> HUGE clouds=> HUGE clouds
Sodium
SodiumMendillo et al.
Krimigis et al.
500 Rj ~ 1/4 A.U500 Rj ~ 1/4 A.U.
ENAsS, O, H
30 Rj 30 Rj
SMall EXplorer mission ~$120M
Earth-orbiting UV telescope to observe Io, the torus and Jovian aurora
JunoJunoJupiter Jupiter Polar Polar
OrbiterOrbiter~$650M
Solar Wind Interaction with a Comet
TIME
EN
ER
GY
EN
ER
GY
H+
Heavy Ions
Comet Borelly
Deep Space 1
Pluto & Charon
The solar wind interacts with Pluto’s escaping atmosphere like a comet
Thank you!
New Horizons 2016
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