Thanks to: Margaret Kivelson David Brain Steve Bartlett Fran Bagenal University of Colorado

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