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Outline. The Outer Heliosphere. The Heliosphere, Astrospheres and the Interstellar Interaction Implications of Recent Voyager Results Energetic Neutral Atoms [ENAs], ENA Imaging and IBEX Science IBEX Flight System, Mission Design, Launch, Orbit and Sky Coverage

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  1. Outline The Outer Heliosphere • The Heliosphere, Astrospheres and the Interstellar Interaction • Implications of Recent Voyager Results • Energetic Neutral Atoms [ENAs], ENA Imaging and IBEX Science • IBEX Flight System, Mission Design, Launch, Orbit and Sky Coverage • IBEX Payload and Instrumentation • IBEX Operations, Broad Science Opportunities and E/PO Robert W. EbertUniversity of Texas at San Antonio/Southwest Research Institute SHINE 2008 Student Day – June 22, 2008Zermatt Resort - Midway, Utah

  2. Outer Heliosphere voyager.jpl.nasa.gov/images/Heliosphere3b.jpg

  3. Outline • Anomalous Cosmic Rays (ACRs) • Recent Voyager Results • Interstellar Boundary Explorer (IBEX)

  4. Anomalous Cosmic Ray (ACR) Basics • ACRs are low energy cosmic rays (~1–100 MeV/nucleon) • They were first discovered in the early 1970’s through an observed “anomalous” enhancement in the low energy helium, nitrogen and oxygen cosmic ray fluxes [Garcia-Munoz et al. 1973; Hovestadt et al. 1973; McDonald et al., 1974]. • Fisk et al. (1974) proposed the source of these low energy cosmic rays to be neutral particles from the local interstellar medium (LISM). • LISM neutrals are swept into the inner heliosphere, subsequently ionized by photo-ionization or charge exchange, picked up by the solar wind and accelerated in the outer heliosphere. • Pesses et al. (1981) proposed that these ionized neutrals were accelerated at the termination shock (TS) by diffusive shock acceleration.

  5. ACR Composition • Source of ACRs from LISM consist of neutrals with a high first ionization potential (FIP) • H+, He+, O+, N+, Ne+, Ar+ have all been observed • Mainly singly charged at low energies • ACRs > 350 MeV become multiply charged [Mewaldt et al. 1996] due to electron stripping during their acceleration [Jokipii 1996; Cummings et al. 2007] • Low FIP ions such as C+, Mg+, Si+, and Fe+ have also been observed from sources within the heliosphere. • Inner source - neutralization of solar wind by dust grains (Gloeckler et al. 2000). • Outer source - dust grains in Kuiper belt [Schwadron et al. 2003]. Cummings and Stone, 1987 • ACR flux and composition information provide a tool to study the abundance, ionization state and isotopic ratio of material in the LISM, the process of ionization by charge exchange and photo-ionization within the heliosphere, and the acceleration efficiency at the TS.

  6. The “Classic” ACR Picture

  7. The “Classic” ACR Picture • Acceleration due to a diffusive process at the TS • long-standing, most viable accelerator • ~1 year needed to create ACR spectrums [Mewaldt, 2006] • Diffusive shock acceleration (DSA) predicts a power law energy spectrum at the source: J (E) = JoE-ɣ From Cummings et al. 2007

  8. Voyager 1 and 2 Spacecraft • In situ observations from Voyagers provide detailed measurements at two specific locations

  9. Voyager 1 Results • Voyager 1 (V1) crossed the TS at 94 AU in late 2004. • TS weak  U1/U2 ~ 2.6 • Energetic particle spectra just past TS • Low energy particles fit power law • High Energy ACRs • Still modulated below ~100 MeV • ACR spectrum not “unfolded” into single power law as predicted Decker et al., 2005

  10. Voyager 2 Results • V2 crossed the TS multiple times at 85 AU in August 2007. • He+ spectrum remained modulated just after TS crossing • V1 currently located in the heliosheath at ~105 AU • He+ ACR spectrum may have unfolded to source spectrum [Cummings et al. 2008] Cummings et al. 2008 – Submitted to 7th IGPP Conference Proceedings

  11. The Voyager ACR Paradox • Voyagers proved that ACRs were not being accelerated by the TS at times and locations where they crossed Major questions: Where and how are ACRs accelerated??? • Interaction of merged interaction region (MIR) with the TS could result in observed intensity decrease [Florinski and Zank, 2006] • Are they accelerated elsewhere on TS [McComas & Schwadron, 2006]? • Are ACRs being accelerated by stochastic processes (second order Fermi) further out, beyond the TS, in the heliosheath [Fisk et al., 2006]?

  12. The Global Heliospheric Interaction • Voyager observations clearly show how little we really know about our local cosmic accelerator • Outstanding local observations relevant to particle acceleration and transport at two specific locations  Local observations beg the question of the global interaction

  13. ENAs Illuminate the Global Termination Shock • Supersonic SW must slow down and heat before it reaches the interstellar medium • Large numbers of interstellar neutrals drift into heliosphere • Ly-a backscatter • interstellar pickup ions • Hot SW charge exchanges with interstellar neutrals to produce ENAs • Substantial ENA signal from outside the TS guaranteed from first principles JENA = dx nH JION

  14. Interstellar Boundary Explorer (IBEX) • NASA funded Small Explorer Mission (SMEX) • Southwest Research Institute (SwRI) is the PI institution • Mission PI – Dr. David McComas • Set for launch Sept. 2008

  15. IBEX’s Sole, Focused Science Objective • IBEX’s sole, focused science objective is to discover the global interaction between the solar wind and the interstellar medium. • IBEX achieves this objective by taking a set of global energetic neutral atom (ENA) images that answer four fundamental science questions: • What is the global strength and structure of the termination shock? • How are energetic protons accelerated at the termination shock? • What are the global properties of the solar wind flow beyond the termination shock and in the heliotail? • How does the interstellar flow interact with the heliosphere beyond the heliopause?

  16. Global ENA Images: Questions I & III • Global ENA images easily differentiate types of TS interactions • Gross Differences: • Upstream/Downstream • Dawn/Dusk • North/South • Subtle asymmetries in global images illuminate flow patterns beyond the termination shock Extremes of differential ENA fluxes from 0.3-0.6 keV predicted for a strong gas-dynamical TS (top) and a TS weakened by a large pickup ion pressure (bottom) [Gruntman et al., 2001].

  17. IBEX Spacecraft & Sensors • Two huge aperture single pixel ENA cameras: • IBEX-Lo (~10 eV to 2 keV) • IBEX-Hi (~300 eV to 6 keV) • Simple sun-pointed spinner (4 rpm)

  18. Interstellar Boundary Explorer Imaging the Edge of Our Solar System and Beyond

  19. Relevant Sessions • What is the Acceleration Mechanism for Anomalous Cosmic Rays and Where is it Happening? • Times: Monday PM, Shine Session 3, St. Moritz Tuesday AM, Shine Session 3, St. Moritz • Session leaders: Alan Cummings (Caltech) Randy Jokipii (U. of Arizona)

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