Dave McComas: 1

IBEX discoveries over a half decade

of observing the outer heliosphere

1 Southwest Research Institute, San Antonio, TX 78228, USA2 University of Texas at San Antonio, San Antonio, TX 78249, USA3 On behalf of the entire IBEX Project and Science Teams

David J. McComas1,2,3

Queenstown, New Zeeland – 2/11/15

Dave McComas: 2

IBEX Mission Summary

• NASA Small Explorer (SMEX)

– PI Mission (SwRI prime)

– ~$100M plus Pegasus launch

– International support: Switzerland,

Poland, Germany, Russia

• Launched 19 October 2008

– ~100 kg, <0.5 m3

– IBEX-developed capability included

~400 kg SRM and adapter

• Launched with cost under run

• Extended Mission since Jan 2011

• >180 Refereed papers and counting

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Our Heliosphere

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Galactic Cosmic Ray Shielding

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ENAs – From the Sun to IBEX

10 billion mile “hole in one”

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ENAs Illuminate Invisible Heliosheath

JENA = dx nH JION

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Voyager 1 & 2 in Heliosheath

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Mollweide all-sky projection showing locations of Voyagers

Voyagers provide detailed information in these two directions

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Independent Confirmation

IBEX-Lo & Hi observations independently confirm ribbon (Hi at ~1.1 keV and Lo at ~0.9 keV shown)

McComas et al., Science 2009

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McComas et al., Science 2009

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Ribbon Correlates with Br=0

Schwadron et al.,

Science 2009

Parker [1961] Interactions

IBEX results indicate both external

forces are important!

McComas et al., Science 2009

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The Start of a New Paradigm

McComas et al., Science 2009

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Science - IBEX Special SectionMcComas et al., First Global

Observations of the Interstellar Interaction from the Interstellar Boundary Explorer

Fuselier et al., Width and Variation of the ENA Flux Ribbon Observed by the Interstellar Boundary Explorer

Funsten et al., Structures and Spectral Variations of the Outer Heliosphere in the IBEX Energetic Neutral Atom Sky Maps

Schwadron et al., Comparison of Interstellar Boundary Explorer Observations with 3-D Global Heliospheric Models

Möbius et al., Direct Observations of Interstellar H, He, and O by the Interstellar Boundary Explorer

Krimigis et al., Imaging the Interaction of the Heliosphere with the Interstellar Medium from Saturn with Cassini

13 November 2009 Issue

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Circularity of the IBEX ribbon

Funsten et al., ApJ, 2013

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Schwadron et al. Science, 2014

Global anisotropies in TeV cosmic rays related to the

Sun’s local galactic environment from IBEX

• IBEX Ribbon (B) and ISN flow direction consistent with interstellar

modulation of TeV CRs and diffusive prop from supernova sources

• Simple model reproduces global anisotropy maps of ground-based high-

energy cosmic-ray observatories (Milagro, Asg, and IceCube)

• Larger local interstellar magnetic field direction consistent with IBEX

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6 of 13 Proposed Ribbon Sources

McComas et al., JGR 2010+7 others…

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More New Ribbon Ideas Emerge

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McComas et al. Rev Geophys, 2014

Model / Scenario Strengths Weaknesses

Inner Heliosheath

IHS 1: Shock-processed

PUIs / ACRs

Produces ring of enhanced 1 keV ENA emissions resembling Ribbon. Relative

intensities of ring and global emissions consistent with observations.

Ordering of Ribbon by draped ISMF not explained. Uses idealized symmetric

TS/HP geometry.

IHS 2: Specularly reflected

SW ions/PUIs

Explains enhancement of Ribbon emissions vis-à-vis globally distributed flux

in terms of well-established shock-physical processes.

Ribbon’s ordering by ISMF not explicitly addressed. Uses ad hoc TS/HP

geometry. LOS path length for global emissions not consistent with estimates

of IHS thickness. Ring-beam distribution of Ribbon ENA source may not be

stable (cf. OHS 2).

IHS 3: Stagnation Region Region of enhanced IHS plasma density to balance external JxB force may

explain Ribbon’s ordering by ISMF and enhanced intensity vis-à-vis global

flux. Possible HP extrusions may explain fine structure.

Does not predict different energy spectra for the Ribbon and global flux. MHD

models including external JxB force do not find enhanced pressure. Stagnation

scenario still requires some missing non-MHD physics.

IHS 4: H-wave Predicts ring-like emission feature ordered by ISMF. Accounts for broadening

of Ribbon at higher energies.

To satisfy B•r=0, assumes that normal of H-wave phase front is not

significantly tilted from ISMF direction. Difference between Ribbon and

global flux energy spectra not satisfactorily explained.

Heliopause

HP 1: Magnetic

Reconnection

Potentially accounts for Ribbon’s ordering by ISMF. May explain Ribbon fine

structure.

Likely to produce multiple distributed source regions instead of continuous

Ribbon owing to alternating IMF polarity.

HP 2: K-H & R-T

Instabilities

May explain Ribbon fine structure. Does not explain Ribbon’s shape and position and may not provide large

enough structures for factor of 2 enhanced flux.

Outer Heliosheath

OHS 1: ISMF Compression Produces Ribbon ordered by draped ISMF as a result of conservation of first

adiabatic invariant / increased density in compressed field region. (Cf. OHS 3)

Assumes unspecified suprathermal source in OHS.

OHS 2: Secondary ENAs Produces narrow Ribbon ordered by draped ISMF. Can reproduce observed

ordering of ENA energies by heliographic latitude.

PUI ring-beam distribution must remain stable against pitch-angle scattering

long enough for re-neutralization to occur.

OHS 3: Magnetic Mirror Produces Ribbon-like structure ordered by draped ISMF from PUIs transported

along ISMF to regions of increased B (magnetic mirror points). (Cf. OHS 1)

Assumes no pitch-angle scattering in OHS as limiting case.

OHS 4: Retention Region Produces Ribbon ordered by draped ISMF. Does not require maintenance of

ring-beam distribution. Reproduces observed ordering of ENA energies by

heliographic latitude.

Includes only neutral SW but not ENAs from IHS source. Modeled Ribbon

thus narrower than observed.

Interface of Local Interstellar Cloud and Local Bubble

ISM 1: LIC/LB Interaction Calculates ENA intensity profiles at 1 keV for viewing geometries that

produce circular emission feature. Intensities are consistent with observations.

Does not explain Ribbon’s apparent ordering by ISMF or features reflecting

solar wind structure and temporal behavior. Overestimates ENA survival

probability, especially for lowest energies.

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Secondary ENAs

Heerikhuisen et al., ApJ 2010

Simulated IBEX Data

McComas et al., Science, 2009; McComas et al., JGR 2010

BUT something missing… still need to solve problem of source PADs

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Latitude-Dependant & Direct Ribbon Source

McComas et al., ApJS, 2012

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Spatial Retention of Ions & the IBEX Ribbon

Schwadron and McComas, ApJ, 2013

Simulation IBEX Data

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Additional Detailed Mechanisms

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Spectral Slopes of ENAs

McComas et al., Science 2009

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Pickup Ions k Distributions

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Livadiotis et al. ApJ, 2013

Pressure of the proton plasma in inner heliosheath

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Zirnstein et al. ApJL, 2014

Multi-component nature of the inner and outer

heliosheath plasma and its effect on ENA flux

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Desai et al. ApJ, 2014

ENAs: Evidence for multiple heliosheath populations

Suggests a significant fraction of ∼0.1–0.5 keV ENAs

may originate from ISNs charge-exchanging with a

non-thermalized (hot) PUIs in the outer heliosheath

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Ribbon/GDF Separation

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Flow Away from Pressure Max

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Heliotail

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McComas et al. ApJ, 2013

The heliotail revealed by IBEX

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Tail Structured by Slow/Fast SW

Starboard

looking

downtail

Port

looking

downtail

E-folding losses

(cooling length)

~100-200 AU

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Local IS Field Twists Heliotail

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Pogorelov et al. ApJ, 2013

Three-dimensional features of outer HSp due to coupling between

the interstellar and interplanetary magnetic fields - Solar cycle

model based on Ulysses obs

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LISM Interaction – Alfven Wings?

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5 Years of IBEX Data

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5-Year Update – ApJS

• Follows on from 2012 ApJS 3 year paper

• Complete and validated observations from first five years (2009-2013) of IBEX mission

• Corrected ENA fluxes– Time-variable CR background (updated)

– Survival prob from outer HSp (orbit-by-orbit)

– New “ion gun” background removal

• ENA maps, data, and supporting documentation full release of these datato broad community and provide the citable reference for data, data processing and use

• Examine time variations in 2009-13 epoch

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Ribbon Discontinuous through Tail

• Tail structure dominates

across the downwind region

with Ribbon continuous

around rest of arc

• If the Ribbon produced by

ENA emissions from the TS or

inner heliosheath, no a priori

reason that similar emissions

would not also arise from the

nearby tailward portions

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Leveling Off of ENA Fluxes

• Heliotail fluxes

continue to drop owing

to greater distance and

longer “recycling” time

for SW ions

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SW Dynamic Pressure and IMF

McComas et al., JGR 2013

Parameter Units 1974-1994 2009-79/2013 Difference Rel. Change

Dyn Press nPa 2.36 1.40 -0.96 -41 %

|BR| nT 3.59 2.23 -1.36 -38 %

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2013 ENAs ~0.7 of 2009

Energy

(keV)

Ratio of weighted fluxes in annual SC Ram maps (Flux2013/Flux2009)

1) Ribbon 2) Nose/Npole 3) S pole/flank 4) Heliotail All Sky

~0.7 0.87 ± 0.01 1.02 ± 0.03 0.85 ± 0.02 0.7 ± 0.02 0.86 ± 0.01

~1.1 0.63 ± 0.01 0.72 ± 0.01 0.67 ± 0.01 0.71 ± 0.03 0.68 ± 0<.01

~1.7 0.75 ± 0.01 0.66 ± 0.01 0.68 ± 0.01 0.66 ± 0.03 0.69 ± <0.01

~2.7 0.73 ± <0.01 0.64 ± 0.01 0.73 ± 0.01 0.64 ± 0.03 0.7 ± <0.01

~4.3 0.65 ± <0.01 0.64 ± 0.01 0.79 ± 0.01 0.62 ± 0.02 0.69 ± <0.01

McComas et al. [ApJS, 2012] predicted 0.72 based on SW data and 2-4 year average time delay for SW ENA recycling

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Recycled Solar Wind

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Ribbon Changes by Region

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Ribbon Emissions over Time

• Leveling off near the nose/south, but continued drop at

higher northern latitudes consistent with a great

distance to the source of the Ribbon around the high

latitude flanks on the downwind side of the north pole

• Consistent with an inner heliosheath or secondary ENA

source at greater distances in the north than south

• Possible issue with the time variation from both the

Ribbon and GDF not generally beginning with the

highest energies (time dispersion)…

But - Möbius et al. [2013] pointed out secondary ENA

Ribbon source might not show owing to more distant

source for higher energies compared to lower energies

could compensate for faster speed of higher energy

ENAs and allow the change in slope or even turn up to

appear to occur simultaneously

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Motions of Sun and Local Clouds

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IBEX ISN Observations

Möbius et al., Science 2009

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Direct Sampling of ISNs

• Ulysses/GAS

– First measurements of He [Witte et al. 2004]

• IBEX – the Interstellar Boundary Explorer

– First measurements of H and O [Möbius et al. 2009]

– First measurements of Ne and the Ne/O ratio [Bochsler et

al. 2012; Park et al. 2014]

– First observation of deuterium [Rodriquez et al. 2013;14]

– Detailed analyses of He [e.g., Möbius et al. 2009; Bzowski

et al. 2012; Möbius et al. 2012; McComas et al. 2012]

– First measurements of secondary O (O from interstellar O+

charge exchange in outer heliosheath) [Möbius et al. 2009]

– Discovery of secondary He population: “Warm Breeze”

[Kubiak et al. 2014]

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Direct Detection of Interstellar Neutrals

• McComas, D.J., Editorial

• Lee, M. et al., An Analytical Model of Interstellar Gas in the Heliosphere Tailored to IBEX Observations

• Hlond, M., et al., Precision pointing of IBEX-Lo observations

• Möbius, E. et al., Interstellar Gas Flow Parameters Derived from IBEX-Lo Observations in 2009 and 2010 -Analytical Analysis

• Bzowski, M., et al., Neutral interstellar helium parameters based on IBEX-Lo observations and test particle calculations

• Bochsler, P., et al., Estimation of the neon/oxygen abundance ratio at the heliospheric termination shock and in the local interstellar medium from IBEX observations

• Saul, L., et al., Local Interstellar Neutral Hydrogen sampled in-situ by IBEX

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McComas et al., Science, 2012

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4-D “Tubes” of Possible Parameters

• Interstellar T and flow speed as functions of ecliptic longitude

• IBEX observations allow narrow “tube” in the 4-D space of the interstellar flow vector and temp

• Shading represents 1possible ranges

ISM 49.71 0.47o cos1(1/(1

REVISM2

GMS

)) 49.71 0.47o cos1(1/(1VISM2

VE2))

tanISM 0.030 0.004 0.073 | sin(ISM 49.71 0.47o) |

)489.05.13(

)(195.290

)(

)(5.290)(

2

10

2

ISM

ISMISM

ISM

ISMISMISM

V

aa

VT

Old

Ulysses

Value

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Zieger et al. GRL, 2013

A slow bow shock ahead of the heliosphere

• Modeled possibility of slow magnetosonic shock

ahead of the heliosphere where angle between the

interstellar magnetic field and the interstellar plasma

flow velocity is quite small (e.g., 15° to 30°).

• Produced spatially confined quasi-parallel slow BS

– Voyager 1 is heading toward while Voyager 2 isn’t

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Leonard et al., 2015 (submitted)

• Lee et al. [2012] analytic model

not good for S/C pointing out of

ecliptic

• In ecliptic consistent values

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Ecliptic Pointing Flow Vectors Converge

McComas et al. [2012] tube still

consistent

McComas et al., ApJ 2015

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…But Requires Much Warmer ISM

Old Ulysses Value

He now isothermal with

O/Ne

McComas et al., ApJ 2015

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Implications

• ~26 km s-1 squarely back between speeds of LIC (~24) and

the G-Cloud (~30) [Redfield & Linsky 2008]

• Reopens question of fast magnetosonic (MS) Bow Shock

– LISM He+ reduces fast MS speed [Scherer and Fichtner 2014]

– Zank et al. [2013] showed shock mediated to wave via charge

exchange and still consistent w/ H wall observations

• Consistent w/ remote sensing observations of warmer ISM

[Redfield & Linsky 2004, Frisch et al., 2014]

– Warmer ISM requires either additional heating from the cloud

interface or reduced cooling rates to maintain LIC equilibrium

• Roughly isothermal for He and O/Ne [Möbius et al. 2014]

• BISM∞–VISM∞ plane consistent w/ Ly-a data [Lallement et al.,

2005] and IBEX Ribbon center

• He distribution complicated, suggesting multi-components

and additional physics needed for lower flux wings

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Rodriquez et al. A&A, 2013

Evidence of direct detection of deuterium in the LISM

We find that D/HLISM =1.6 ± 1.2 × 10−5, which agrees with

D/HLIC = 1.6 ± 0.4× 10−5 for the local interstellar cloud

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ISN Current Status

• IBEX has made groundbreaking first observations and

discoveries about numerous interstellar neutral species

• Tight coupling of possible He inflow speed, longitude,

latitude, and temperature along narrow 4-D “tube”

• 2012-2014 ecliptic pointing data indicate region along

“tube” is close to Ulysses speed/angles, but much hotter

• Recommend combined IBEX/Ulysses values of VISM∞ ~26

km s-1 , ISM∞ ~75°, ISM∞ ~ -5°, and THe∞ ~7000-9500 K.

• Heliosphere in substantially warmer region of ISM that

may be roughly isothermal (O/Ne temperatures similar)

• Complicated non-Maxwellian distributions and possible

multiple populations (e.g., “Warm Breeze” [Kubiak et al.

2014])… much more to discover!!!

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First: Neutral Atoms from Moon

First Observations of Neutralized/Reflected Solar Wind from Lunar Regolith

ENA Albedo ~ 10%

Moon Emits ~150

ton/yr of Hydrogen

McComas et al., GRL 2009

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Firsts: Dayside Magnetosphere

Northern cusp

emissions

Southern cusp

emissions

Magnetopause emissions

First ENA imaging of Magnetopause:

Fuselier et al., GRL 2010

First ENA imaging of Cusps:

Petrinec et al., JGR 2011

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First: Plasma Sheet Images

Orbit 52

McComas et al., JGR 2011

Orbit 51

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New IBEX Orit Stable to >2050

• Discovery of new class of long term stable lunar-synch orbits

• June of 2011 - successful IBEX maneuver into new orbit

IBEX’s journey of discovery continues…

McComas et al., Space Weather 2011

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