Outline

■ 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/POSHINE 2008 Student Day – June 22, 2008

Zermatt Resort - Midway, Utah

SHINE 2008 Student Day – June 22, 2008

Zermatt Resort - Midway, Utah

Robert W. EbertUniversity of Texas at San

Antonio/Southwest Research

Institute

Robert W. EbertUniversity of Texas at San

Antonio/Southwest Research

Institute

The Outer HeliosphereThe Outer Heliosphere

Outer Heliosphere

voyager.jpl.nasa.gov/images/Heliosphere3b.jpg

Outline

■ Anomalous Cosmic Rays (ACRs)■ Recent Voyager Results■ Interstellar Boundary Explorer (IBEX)

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.

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.

The “Classic” ACR Picture

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

Voyager 1 and 2 Spacecraft

■ In situ observations from Voyagers provide detailed measurements at two specific locations

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

Voyager 2 Results

Cummings et al. 2008 – Submitted to 7th IGPP Conference Proceedings

■ 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]

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]?

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

■ Supersonic SW must slow down and heat before it reaches the interstellar medium

■ Large numbers of interstellar neutrals drift into heliosphere● Ly- 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

ENAs Illuminate the Global Termination Shock

JENA = dx nH JION

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

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:

I. What is the global strength and structure of the termination shock?

II. How are energetic protons accelerated at the termination shock?

III. What are the global properties of the solar wind flow beyond the termination shock and in the heliotail?

IV. How does the interstellar flow interact with the heliosphere beyond the heliopause?

Global ENA Images: Questions I & III

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].

■ 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

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)

Imaging the Edge of Our

Solar System and Beyond

Imaging the Edge of Our

Solar System and Beyond

Interstellar Boundary Interstellar Boundary ExplorerExplorer

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)