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Voyager 1’s Dec. 2004 Termination Shock Crossing and Energetic Neutral Atoms

Voyager 1’s Dec. 2004 Termination Shock Crossing and Energetic Neutral Atoms. Christina Prested, Boston University Shine 2007, July Student Day, July 29 Whistler, Canada. Outline. Edge of the Solar System -Local Interstellar Medium (LISM) -Termination Shock (TS) and Heliosheath

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Voyager 1’s Dec. 2004 Termination Shock Crossing and Energetic Neutral Atoms

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  1. Voyager 1’s Dec. 2004 Termination Shock Crossingand Energetic Neutral Atoms Christina Prested, Boston University Shine 2007, July Student Day, July 29 Whistler, Canada

  2. Outline Edge of the Solar System -Local Interstellar Medium (LISM) -Termination Shock (TS) and Heliosheath -Voyager 1 results Energetic Neutral Atoms (ENAs) -Production -Heliospheric ENAs distribution, TS properties Interstellar Boundary Explorer (IBEX) -Mission & science objectives - Other ENA sources & foreground

  3. Local Interstellar Medium · Solar System imbedded in cloud of gas · n ~ 0.1 cm-3, partially neutral · T ~ 6500 K · 26 km/s w.r.t. Sun Image: IBEX

  4. The Edge of the Solar System · Supersonic solar wind + LISM = TS · Heliosheath & Hydrogen wall · Heliopause · Direction of LISM magnetic field mostly unknown -effects shape and location of TS · Bow Shock

  5. ρ2>ρ1 p2 ρ1 p1 v1 v2 B1 B2 Rankine-Hugoniot Conditions for MHD shock* Conservation of: mass, magnetic flux momentum energy *Obliqueness adds complexity

  6. Voyager 1 & 2 probe the outer edge of the solar system 2005 locations (HGI): V1: 94 AU 34.1 ° N, 172.3° V2: 75 AU 25.76 ° S, 215.6° Image: NASA

  7. How we know V1 crossed the TS B increase ~2-4 (conservation of magnetic flux) Intensity of ‘low’-energy particles abrupt increase (conservation of mass & beaming)

  8. How we know V1 crossed the TS Change in properties of the turbulence Plasma waves characteristic of shock crossings (electron foreshock)

  9. What was discovered about TS · 94 AU · Non-static -2000-2004 anti-sunward motion -2004-2005 sunward motion · Weak shock; U1/U2 = r = 2.6 +0.4/-0.2 · TS not source of Anomalous Cosmic Rays (at least locally) · Likely asymmetric due to LISM B field A single data point does not define the global and transient system

  10. ENA production in the Heliosheath SW is shock heated by TS Hot H+ charge exchanges with LISM neutrals to produce hot H ENA population depends NP, NA, f -> TS properties (strength, position)

  11. ENA distributions ·Distribution ENAs how we understand TS ·Kappa distribution is better fit than Maxwellian distribution · Ubiquitously found in space plasmas · V1 measures κ ~ 1.6 · Significantly impacts ENA flux

  12. IBEX Mission Overview • ·Launch: June 2008 • ·Measure ENA flux to answer: • What is the global strength and structure of the termination shock? • ·High and Lo energy sensors have 14 E channels (.01-6 keV) IBEX, 2007

  13. Foreground and sources of ENAs (.01 to 6 keV)* *non Heliospheric Sources (minus foreground): Steve Fuselier, IBEX Noise and Background Doc.

  14. Synthetic Flux Maps of Heliosphere

  15. Conclusions · TS produced by LISM interaction with SW · Shock heated SW charge exchanges with LISM neutrals to produce Heliospheric ENAs · Distribution of ENAs connected to TS properties · IBEX will image Heliospheric ENAs to discover global properties of TS · ENA foreground is negligible if Magnetospheric ENAs excluded

  16. References http://www-ssg.sr.unh.edu/ism/LISM.html McComas et al., The Interstellar Boundary Explorer, Physics of the Outer Heliosphere, Third International IGPP Conference, 2004 http://www.ibex.swri.edu http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html Voyager Science Special Issue, 2005 Fisk & Gloeckler, 2006

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