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 2
... and rotating
All planetary objects
probably have enough
rotation - the presence
(or not) of a global
magnetic field tells us
about
1 and 2
1
Magnetospheres of the Giant Planets
Scales
• LARGE
Earth
• Rotating with planet
• Jupiter + Saturn:
• dipole with small tilt
• dynamo in metallic hydrogen
• Uranus + Neptune:
• multipole, large tilt
• dynamo in water/ammonia/methane
Mercury & Ganymede
Mercury - Magnetic field
detected by Mariner 10 in 1974
Ganymede - Magnetic field
detected by Galileo in 1996
Solar
Wind
Bsurface ~ 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
+S
is the ability toFeexplain
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
HST
observations
of oxygen
emissions
- McGrath
Aurora on Ganymede
Trailing Side
= Upstream
North Polar Cap
Leading Side =
Downstream
South Polar Cap
Khurana & Pappalardo
Mars Global Surveyor
Magnetometer - 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
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
PSolar Wind =
P (magnetic)crust
+ P (thermal)ionosphere
David Brain
Mars’Interaction Boundary
Response to the Solar Wind
QuickTime™ and a
GIF decompressor
are needed to see this picture.
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
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Over a Strong Magnetic Region
QuickTime™ and a
GIF decompressor
are needed to see this picture.
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
Callisto
Fran Bagenal
Think of a moon embedded in a plasma which overtakes
the moon in
the direction of its orbital motion.
University of Colorado
Europa & Callisto
Radiolysis - Bombardment of surface
and minerals by
“Because of the ices
magnetosphere,
the
energetic
particles
Galilean satellites
have all
lost thefrom
the magnetosphere
equivalent of a Titan
(or Earth)
- changes
chemistry
atmosphere over the
past grain
billion
- alters
size
- embedded heavy ions
years”
- sputtering
THEN - the
- Bob Johnson
Galileo Near InfraRed Mapping atmosphere is ionized
Spectrometer image of Europa
showing distribution of hydrated & stripped away by
sulfur compounds
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
Io
300 km
Amirani
Io’s
Volcanoes
& Geysers
Pilan Plume
Prometheus
Pilan 5 months apart
Infrared glow
Pele
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 UltraViolet Imaging Spectrometer
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.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
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
Aurora
Jupiter’s attempt
to spin up its
magnetosphere
Main Oval
Io footprint + wake
G
E
Clarke et al.
Jupiter’s Extended Corona
ENAs
S, O, H
Charge exchange of
energetic charged
particles with neutral
clouds around orbits of
Io and Europa ->
escaping Energetic
Neutral Atoms
30 Rj
Krimigis et al.
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
Comet Borelly
Heavy Ions
H+
TIME
Deep Space 1
Pluto & Charon
The solar wind interacts with Pluto’s escaping
atmosphere like a comet
New Horizons 2016
Thank you!