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Jupiter s Dust Disc An Astrophysical Laboratory

Jupiter s Dust Disc An Astrophysical Laboratory Harald Krüger MPI für Sonnensystemforschung, Katlenburg-Lindau, Germany MPI für Kernphysik, Heidelberg, Germany Images: NASA/JPL Outline Introduction: Why
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Jupiter s Dust Disc An Astrophysical Laboratory Harald Krüger MPI für Sonnensystemforschung, Katlenburg-Lindau, Germany MPI für Kernphysik, Heidelberg, Germany Images: NASA/JPL Outline Introduction: Why dust? How do we study space dust? Galileo/Ulysses in situ dust measurements at Jupiter: - Electromagnetically interacting dust streams - Dust clouds at the Galilean moons, tenuous Galilean dust ring - Galileo passages through Jupiter s Gossamer rings The Cosmic Cycle of Matter Condensation interstellar clouds of gas and dust Star formation Hot bubbles und dust Winds and supernova explosions of stars compact stars Stars and planets The cosmic cycle of matter: Heavy elements are produced in stars and supernova explosions and ejected into interstellar space They form building blocks for the next generation of stars and planets. Also our solar system including the Earth was formed from such primitive matter. Why Dust? Dust particles are messengers and intimate players in cosmic processes, e.g. proto-planetary accretion disks and formation of planetesimals Like photons, dust carries information about its formation and history ('Dust Astronomy') Study of dust in space can provide important information on fundamental processes governing the formation of planetary systems Dust in a planetary system is the most processed of the different populations of cosmic dust Dust displays its presence impressively as cometary dust tails, the zodiacal light and 'dusty' planetary rings Dust is produced by endogenic and exogenic processes: collisions, condensation, sublimation, etc. In a dusty plasma dust traces plasma and magnetospheric conditions (charged dust behaves like ions in a magnetosphere). Solar system and planetary dust discs at Jupiter and Saturn are ideal places to study many of these processes Dust: A Tool to Study Astrophysical Processes Galileo Spacecraft Nasa/JPL Galileo/Ulysses In-Situ Dust Detectors Multi-coincidence impact ionization detector 0.1 m² sensitive area 140 field of view Measurement of mass, speed and impact direction Mass range: kg (~ µm radii) Speed range: 2-70 km s - 1 Dust at Jupiter Voyager 1/2 Discovery of active volcanism on Io Can dust condensing in Io's plumes escape from Io? (Johnson, Morfill and Grün, 1980) Plumes Nasa/JPL Ulysses First Solar Orbit ESA The Jovian System as a Source of Dust Streams of electrically charged dust grains emanating from the jovian system (Grün et al., 1993) 26 day periodicity Interaction with interplanetary magnetic field (Hamilton & Burns, 1993) Grain radii ~ 10 nm, speeds 300 km/sec (Zook et al., 1996) Jupiter s magnetosphere: giant dust accelerator Confirmed during 2 nd Jupiter flyby of Ulysses in 2004 (Krüger et al., 2006) Stream formation connected with interaction with CIRs and CMEs (Flandes et al., 2011) Ulysses (Grün et al. 1994) Correlations with IMF Magnetic Field: Red: B r points sunward Blue: B r points anti-sunward Dust: (Krüger et al. 2006) Vertical bars: 1σ standard deviation Correlations with IMF Dust streams detected in 2004 (-9 β ecl +10 ; -20 β jup +70 ) Deviation of streams from Jupiter line-of sight direction correlates with B field! (Krüger et al. 2006) Galileo at Jupiter NASA/JPL Electromagnetically Interacting Dust at Jupiter 5 and 10 hour periodicities: dust impact rate correlated with Jupiter s 10 hour rotation period grains strongly coupled to Jupiter s magnetic field. (Grün et al. 1998) Jupiter Dust Streams: Electromagnetically Interacting Dust 5 and 10 h periodicities: dust particles couple with jovian magnetic field ~ 42 h periodicity imposed by Io's orbital period (Io signature) Io acts as point source for dust particles (Graps et al. 2000) Jupiter's Magnetosphere: A Giant Mass Spectrometer Grains released from Io source Charged to +5 V in plasma torus (secondary electron emission) Accelerated by co-rotational electric field Size- dependent dynamics: - s 200 nm: captured by Jupiter's grav. field - 9 s 200 nm: escape from Jovian system - s 9 nm: captured by Jupiter's magn. field Main acceleration within ~ 10 R J from Jupiter (Horanyi et al. 1993,1997, Hamilton & Burns, 1993; Grün et al. 1998) Jupiter s Dusty Ballerina Skirt Horanyi 2000 Jupiter s Dusty Ballerina Skirt Horanyi 2000 Dust Streams: A Monitor of Io's Volcanic Activity NASA/JPL Io, Galileo Dust Streams: A Monitor of Io's Volcanism Average Io dust emission ~ kg s -1 Small compared to ~ 1 ton s -1 of plasma ejected Strong peaks in dust emission coincide with largest surface changes Dust condenses in Io s plumes Io, Galileo NASA/JPL Krüger et al., 2003 Cassini Cosmic Dust Analyser Impact Ionisation Detector Sensor area 0.1 m 2 Mass, speed, impact direction, charge, composition Calibrated: km s -1 Grain sizes: ~ µm CDA 24 Srama et al Cassini NASA/JPL Mittwoch, 10. August 2011 Composition of Io Dust Grains 287 Cassini mass spectra measured within 1 AU of Jupiter NaCl main constituent of grains (consistent with thermochemical condensation models, Schaefer & Fegley 2005) S other important component (also observed in volcanic plumes, Spencer et al. 1996) K minor component Low silicate component Postberg et al., 2006 Dust Measurements at the Galilean Moons Dust detector Sterne & Weltraum Dust Clouds Surrounding Galilean Moons Dust concentrations detected within the Hill spheres of the Galilean moons. Grains ejected from surfaces by impacts of interplanetary micrometeoroids. Most grains follow ballistic trajectories forming dust clouds around the moons. Europa, Ganymede, Callisto consistent with solid ice-silicate surface (Io fluffier?). All celestial bodies without an atmosphere surrounded by a dust cloud. Analysis of grains can provide compositional information of the moons. Io Europa Ganymede Callisto Krüger et al. 1999, 2003; Krivov et al., 2002; Sremcevic et al., 2003 Tenuous Galilean Dust Ring At least two dust populations identified between Galilean moons ( ~ 6-30 R J ): Prograde grains ejected from Galilean moons (Krivov et al. 2002) Retrograde grains captured by Jupiter's magnetosphere (Colwell et al. 1998) Sizes: ~ µm Ring normal optical depth: τ 10-9 (i.e. not optically detectable) Mass distribution Krüger et al Krivov et al., 2002 Jupiter s Gossamer Rings Voyager image Showalter et al., Nature, 1985 Jupiter s Gossamer Rings From Ockert- Bell et al., 1999 Vertical Extension of Gossamer Rings Particles released from Amalthea are distributed along Amalthea s orbit Burns et al., 1999 Jupiter s Gossamer Rings Main ring and Halo Amalthea ring Thebe ring Thebe extension Metis and Adrastea orbit Amalthea orbit } Thebe orbit Burns et al., 1999 Main ring structures: main ring and halo, Amalthea and Thebe rings (Burns et al., 1999; depater et al., 1999, Ockert-Bell et al., 1999) Most structures constrained by orbits of small moons Adrastea, Metis, Amalthea and Thebe Ring particles are ejecta from small inner regular moons. Grain sizes 5-10 µm, normal optical depth (Showalter et al., 2008) Ejecta particles move inward under Poynting-Robertson drag (Burns et al., 1999) Unexplained outward protrusion called Thebe extension. Galileo Gossamer Ring Passages Main ring and Halo Amalthea ring Thebe ring Thebe extension } Metis and Adrastea orbit Amalthea orbit Thebe orbit Galileo trajectory Two Galileo ring passages in 2002 and 2003 Gossamer Ring: Dust Impact Rate Submicron First gossamer ring passage Micron-sized Drop in dust impact rate Drop in dust impact rate Dust beyond optically detected gossamer rings Krüger et al., 2009 Second gossamer ring passage Drop in dust impact rate Drop in dust impact rate Gossamer Ring Size Distribution Krüger et al., 2009 Size distributions similar in Thebe ring and Thebe extension (slope -0.3) Steepest slope in Amalthea ring (slope -0.6) Grain sizes µm (factor 10 smaller than seen on images) No particles bigger than ~ 4 µm detected because of dust instrument degradation Gossamer Ring Size Distribution Relative number density This work Showalter et al, 2008 Brooks et al., 2004 Krüger et al., 2009 Results of Brooks et al. (2004) are for the main jovian ring! Vertical axis in arbitrary units! Curves are shifted so that they fit at 3 µm. Gossamer Ring: Grain Dynamics Simulation for 3.2 µm dust grains. Variable particle charging on day and night side of Jupiter (shadow resonance; twocompoent plasma model). Semimajor axis and eccentricity increase (plasma density 2.0 cm -3 ). Inner boundary at ~ 2.7 RJ. Q = a(1+e); q = a(1-e); a = semimajor axis. Plasma density critical parameter: ne 0.5 cm -3. Explains Thebe Extension. No Amalthea extension because e/m force weaker at Amalthea, particles recollide more efficiently with Amalthea than with Thebe and Amalthea ring brighter than Thebe ring. Hamilton & Krüger, Nature, 2008 Shadow resonance is a pure electromagnetic effect! Gossamer Ring Results (1) Ring structure measured outside 2.37 R J from Jupiter (dust number density, grain sizes, impact direction, etc.). Grain size distribution: µm, extends known size distribution by an order of magnitude towards smaller particles than previously derived from imaging. Small particles ( 1 µm) dominate dust number density. Large particles (~ 5 µm) dominate optical cross-section. In-situ measurements are sensitive to small particles (with inclinations up to 20 o ) while images see only large grains which are concentrated along the ring plane. Gossamer Ring Results (2) Large drop in particle flux interior to Thebe s orbit. Steeper grain size distribution in Amalthea ring than further out. Variable positive and negative dust charge at day and night side of Jupiter (shadow resonance) accounts for these observations. Model accounts for all major observed stuctures. We now have a consistent picture for the gossamer ring particle dynamics! Electromagnetic forces important in shaping Jupiter s gossamer ring! Jupiter s Dust Disc We have learnt a lot about the distribution, dynamics and transport of dust in the jovian system from Galileo. But we know almost nothing about grain composition! Summary Dust Astronomy: dust grains provide information about their origin and evolution, e.g. formation of planetary systems. Grain trajectories, mass, speed, (composition, charge) can be measured in situ. Electromagnetic interaction of charged grains with the jovian and the interplanetary magnetic fields (dust streams). Jupiter s moon Io is a source for 10 nm dust stream particles. Dust streams: monitor of Io s volcanic activity. Collisional ejection of dust grains from the Galilean moons. Electromagnetic interaction important in shaping Jupiter s gossamer rings. Outlook Outlook JUICE/JGO Dust Telescope JUICE/JGO Dust Telescope JUICE/JGO Dust Telescope Trajectory Sensor: Charge induction Down to 0.1 fc Mass Analyser: Impact Ionisation ToF spectrometer Reflectron Mass resolution ~ 100 LEOPARD-Spektrometer Thank you!
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