Transcript Powerpoint
Fran Bagenal University of Colorado Thanks to: Margaret Kivelson David Brain Steve Bartlett
The Space Environment of Planets
Ganymede, Mercury
- what a magnetic field says about a core - magnetosphere within a magnetosphere
Mars
- surface magnetization - atmospheric loss
Europa, Callisto
- radiation of surfaces - induction in conducting shell -> water
Io
- volcanism, patchy atmosphere - aurora
Comets + Pluto
Planetary Dynamos
Volume of electrically conducting fluid ... which is convecting ... and rotating
2 1 All planetary objects probably have enough rotation - the presence (or not) of a global magnetic field tells us about 1 and 2
Earth
Magnetospheres of the Giant Planets
Scales
• Rotating with planet • Jupiter + Saturn: • dipole with small tilt • dynamo in metallic hydrogen • Uranus + Neptune: • multipole, large tilt • dynamo in water/ammonia/methane layer
Mercury & Ganymede
Mercury - Magnetic field detected by
Mariner 10
in 1974 Ganymede - Magnetic field detected by
Galileo
in 1996 Solar Wind
B surface ~ 1/100 Earth Diameter of Earth
Mercury & Ganymede
What drives convection in these small bodies?
Iron Core -Liquid?
“The test of a good theorist Liquid is the ability to explain any Core outcome, even when the data are wrong” - David Stevenson Liquid Iron Core
Ganymede: A Magnetosphere within a Magnetosphere
Torrence Johnson
Ganymede’s mini-magnetosphere controls the motion of energetic charged particles
Ambient magnetic field Closed Ganymede magnetic field lines Magnetic field coupling Ganymede to Jupiter
Kivelson et al. 1996
Open-closed boundary
Aurora on Ganymede HST observations of oxygen emissions
- McGrath
South Polar Cap Trailing Side = Upstream North Polar Cap Leading Side = Downstream
Khurana & Pappalardo
Mars Global Surveyor
Magnetometer - PI: M. Acuna
Magnetization of surface rocks
No core dynamo today
Magnetization only of old, cratered terrain -> Dynamo ceased ~3.5 billion years ago
Ionosphere
Atmospheric Loss Processes
Neutral Ion
Bulk removal “stripping” Ion pickup Photochemical loss Sputtering
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 P Solar Wind = P (magnetic) crust + P (thermal) ionosphere
David Brain
Mars’Interaction Boundary Response to the Solar Wind
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Field Topology
Solar wind and magnetic field impinging on Mars’ complex magnetic field Close-up of strong anomaly region
David Brain
Changing Topology of Mars’ Magnetic Field
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Over a Strong Magnetic Region
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Mars Aeronomy Mission
Upper atmosphere Ionosphere Magnetic Field Pick-Up Ions Solar Wind
Galileo Mission
The Galilean Satellites
Io
The Magnetosphere
Title
of Jupiter
Europa Ganymede
New Perspectives from Galileo and Cassini
the direction of its orbital motion.
Callisto
Fran Bagenal University of Colorado
Europa & Callisto
Radiolysis years” Bombardment of surface “Because of the magnetosphere, the Galilean satellites have all lost the equivalent of a Titan (or Earth) atmosphere over the past billion - embedded heavy ions - sputtering - Bob Johnson
Galileo
Near InfraRed Mapping Spectrometer image of Europa showing distribution of hydrated sulfur compounds
atmosphere is ionized & stripped away by the magnetosphere
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
Amirani 300 km
Io
Io’s Volcanoes & Geysers
Pilan Plume Infrared glow Pele Prometheus Pilan 5 months apart
Io at night -
Galileo
visible image Glowing Lava Plume Gas & Dust + Aurora
After Spencer & Schneider 1996
Plasma collides with atmosphere on the flanks
Io-plasma interaction: HST data vs model
Jupiter Flow 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
Io Plasma Torus - ground-based telescope
S +
Source of plasma = 1 ton of sulfur and oxygen ions per second
Schneider & Trauger
Cassini U
ltra
V
iolet
I
maging
S
pectrometer
Larry 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.
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E
= direction of dipole tilt
W
brighter
Early Radio Observations &
Radio Beam
Explanations
Dulk (1965) Goldreich & Lyndon-Bell (1969)
The Io Aurora
Infrared
Io Footprint Aurora
Ultraviolet
- energetic particles bombard atmosphere - ‘wake’ emission extends half way around Jupiter
The aurora is the signature of Jupiter’s attempt to spin up its magnetosphere
Main Oval
Aurora
Io footprint + wake G E
Clarke et al.
Jupiter’s Extended Corona
ENAs S, O, H
30 Rj
Krimigis et al.
Charge exchange of energetic charged particles with neutral clouds around orbits of Io and Europa -> escaping
E
nergetic
N
eutral
A
toms Sodium 500 Rj ~ 1/4 A.U
.
=> HUGE clouds
Sodium
Mendillo et al.
SMall EXplorer mission ~$120M Earth-orbiting UV telescope to observe Io, the torus and Jovian aurora
Juno
Jupiter Polar Orbiter
~$650M
Solar Wind Interaction with a Comet
TIME
Comet Borelly
Heavy Ions H +
Deep Space 1
Pluto & Charon
The solar wind interacts with Pluto’s escaping atmosphere like a comet
New Horizons 2016 Thank you!