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 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!