The Magnetosphere The Magnetosphere Title of of Jupiter Jupiter New New Perspectives Perspectives from from Galileo Galileo and and Cassini Cassini Fran Fran Bagenal Bagenal University University of of Colorado Colorado.
Download ReportTranscript The Magnetosphere The Magnetosphere Title of of Jupiter Jupiter New New Perspectives Perspectives from from Galileo Galileo and and Cassini Cassini Fran Fran Bagenal Bagenal University University of of Colorado Colorado.
The Magnetosphere The Magnetosphere Title of of Jupiter Jupiter New New Perspectives Perspectives from from Galileo Galileo and and Cassini Cassini Fran Fran Bagenal Bagenal University University of of Colorado Colorado Comparative Magnetospheres Testing our understanding of SunEarth connections through application to other planetary systems Earth ~ Dipole Rmp ~ (rV2)-1/6 Compressibility 10 R E solar wind rV2 Jupiter Rmp ~ (rV2)-1/3 100 RJ solar wind rV2 Earth ~ Dipole Rmp -> 0.7 Rmp compress 2 7R E solar wind rV2 Jupiter Rmp -> 0.5 Rmp 50 RJ solar wind rV2 Factor ~10 variations in solar wind pressure at 5 AU > observed 100-50 Rj size of dayside magnetosphere b <<1 b ~10 b = nkT B2 /8p Ganymede Io Europa Callisto 1 ton / sec Galileo Mission Galileo Spacecraft spins 3 rpm Voyagers Pioneers Solar Wind Galileo Orbiter 33 orbits Dec. 1995 to Sep. 2003 Cassini flyby Dec. 2000 Ulysses SOLAR WIND Rotation + Outflow EARTH Solar Wind Driven Convection Solar Wind Strong magnetic field 10 hour rotation period Internal plasma source Equatorial plasma disk Corotation with Jupiter Slow outward transport Jupiter - Momentum Coupling • As plasma from Io flows outwards its rotation decreases Khurana 2001 (conservation of angular momentum) • Sub-corotating plasma pulls back the magnetic field • Curl B -> radial current • J x B force enforces rotation Field-aligned currents couple magnetosphere to Jupiter’s rotation Cowley & Bunce 2001 Disks, B, Stellar Rotation, & Jets John Bally Global Structure & Dynamics • Galileo - Survey of magnetic field in the equator -> structure and current systems Jupiter-like Rotation modifies structure at Jupiter Earth-like Khurana 2001 Global Structure & Dynamics Flow Pattern in the Equator • In situ plasma measurements Bursts Superrotation EPD data • Rotation dominates to >140 RJ Krupp et al. • Local time asymmetry • Observed flow pattern consistent with MHD simulations but ~1.5 times stronger. • Abrupt bursts MHD simulation Ogino et al. Global Dynamics - Outstanding Questions •What happens in the magnetotail? • What happens above the equator? • How is angular momentum transferred from Jupiter to the magnetosphere? • What are the roles of Io’s volcanism vs. solar wind in magnetospheric variability? •What triggers disruptions? Vasyliunas 1983 Satellites in the Magnetosphere Ganymede Europa & Callisto • Dynamo in iron core • Magnetosphere within a magnetosphere • Radiolysis of surface Galileo NIMS IR image • Currents induced by changing field indicate liquid water layer Io 300 km Amirani After quantities of lava are removed from below, the crust cracks and tilts, making tall, blocky mountains. 11 km high Hiiaka Patera Tvashtar 50 km Io’s Volcanoes & Geysers Pilan Plume Prometheus Pilan 5 months apart Pele InfraRed Galileo - Nightside of Io - Visible Glowing Lava Plume Gas & Dust + Aurora After Spencer & Schneider 1996 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 UV Warm Torus: 90% of plasma Ne~2000 cm-3 O+ S++ Ti~100eV Te~5eV UV power ~ 2 x 1012 W Cold Torus: Ne~1000 cm-3 S+ Ti~Te~1 eV Source: Extended clouds O, S, SO, SO2, S2..? ~1 ton/s ~3 x 1028 ions/s Dn/n~2% per rotation Local Io Source? ~20%? Io Plasma Torus (Schneider & Trauger) S+ Io Plasma Torus Cassini UVIS - PI Larry Esposito, University of Colorado • Movie - 45 days as Cassini approached Jupiter • Integration over multiple lines in the EUV E = direction of dipole tilt W brighter S++ Emission Image of Torus in O+ Emission Jupiter’s Aurora 110° 200° 290° Wavelength Steffl How do composition, temperatures and UV power vary? Cassini UVIS Steffl 600A 1900A How do composition, temperatures and UV power vary? Steffl 1 3 Tera Watts 2 S+++ S++ O O++ S+++ S+ Oct 2000 Jan 2001 Apr Models of Torus Chemistry Neutral Cloud Theory: Atomic data issues Source = atomic O, S Ionization, Charge Exchange, Recombination Radiative Cooling Ion-Electron coupling - Coulomb collisions Electron heating: Necessary to provide UV emitted power Usually specified as Fhot=Nehot/Necold and Thot Barbosa, Shemansky, Smith&Strobel, Schreier et al., Lichtenberg, Delamere Energetic Particle Recycling After Thorne (1983) 3Energetic - Energetic Particle Particle Recycling Recycling After Thorne (1983) Energetic Particle Recycling • Energetic Neutral Atoms charge exchange S+ + O -> O+ + S* Cassini MIMI • 50-80 KeV/nucleon • Few % of torus’ 1 ton/sec • Re-ionization of fast neutral wind • Cassini/MIMI saw pick-up ions > 2 AU from Jupiter • H+, He++, He+, O+, S+ Molecules?! Krimigis et al. Energetic Particle Recycling Extended Fast/Energetic Neutral Wind • Sodium - ground-based telescopic observations of scattered sunlight - cold neutral wind from chargeexchange of torus ions Sodium Mendillo et al. •MIMI observations of hot neutral sulfur and oxygen (molecules?) from chargeexchange of radiation belt particles >2 AU away Krimigis et al. Jupiter Radio Emission Discovered in 1955 Early Discoveries Io Phase B A B A A B Longitude Io’s Orbital Period = 42 hours Jupiter’s Spin Period = 10 hours Jupiter’s Radio Emission Controlled by - Location of Io - Magnetic Longitude Early Explanations Goldreich & Lyndon-Bell (1969) Dulk (1965) 1979 Voyager flyby The Io Alfven Wave Looking From Side Io’s motion through Jupiter’s magnetic field induces strong electrical currents which propagate as MHD waves along the field lines towards Jupiter. Looking Upstream Voyager Radio Discoveries Voyager PRA Warwick et al. 1979 • Repeated patterns of arcs in frequency-time spectrographs Carr et al. 1983 • Indicates systematic beaming pattern, controlled by the geometry of Jupiter’s magnetic field. Alfven Wave Theory • Io generates Alfven waves • Pattern of reflected waves carried downstream by corotating magnetospheric plasma • Each Alfven wave excites an arc of radio emission. Gurnett & Geortz 1982 • Nice idea—but probably little wave power reaches high latitudes. Galileo Io Flyby - 1995 Fresh hot ions Galileo Electron Beams Connerney et al. The Io Aurora Infrared Io Ultraviolet - energetic particles bombard atmosphere - ‘wake’ emission extends halfway around Jupiter Clarke et al. Io Plasma-Atmosphere Interaction • Electrodynamics: Induction and Pick-up currents deflect flow • Heating, ionization and charge-exchange in atmosphere • Cooling, deceleration of upstream plasma • Acceleration of downstream plasma • Messy! Saur et al. 2002 Delamere et al. 2003 What happens between the torus and Jupiter where the density is very low? Phase II: Pick-up of New Plasma in Io’s Wake • Coupling to torus plasma • Alfven travel-time to “edge” of torus • Acceleration to few% of corotation • 2-D MHD in nonuniform background plasma Delamere et al. 2003 Lessons from FAST at Earth Ergun et al. Ergun et al. EARTH Su et al. 2003 JUPITER 1-D Vlasov code Clarke et al. Aurora Dusk Distortion? Polar storms - Solar Wind Generated? Main Oval Io footprint The aurora is the signature of Jupiter’s attempt to spin up its magnetosphere Aurora Clarke et al. How does UV power of the torus and aurora vary? Tera Watts TORUS TORUSPOWER POWER AURORAL POWER Oct 2000 Jan 2001 Apr The Jupiter-Io System: The Big Picture Although the phenomena shown here have been well studied individually, the causeand-effect relationships between them have not been established. The Jupiter-Io system is a complex interconnected system. SMEX mission Trying Again! Earthorbiting UV telescope to observe Io, the torus and Jovian aurora Juno Jupiter Polar Orbiter Jupiter Polar Mission • Moving beyond initial exploration to address focused questions • Challenging understanding of fundamental magnetospheric processes by exploring different parameter regimes • Reconnection • Cross-field diffusion • Alfvenic acceleration • Parallel electric fields • Cross-scale coupling • Momentum transfer By testing our understanding of concepts developed at Earth through exploring the magnetosphere of Jupiter we open our eyes and see our own magnetosphere in a different light. Galileo: The End Game Sun • Must never hit Earth • Must never hit Europa • Sent into Jupiter Sept. 21st 2003 100 Rjupiter Let’s Keep Exploring!