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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
Dave McComas: 3
Our Heliosphere
Dave McComas: 4
Galactic Cosmic Ray Shielding
Dave McComas: 5
ENAs – From the Sun to IBEX
10 billion mile “hole in one”
Dave McComas: 6
ENAs Illuminate Invisible Heliosheath
JENA = dx nH JION
Dave McComas: 7
Voyager 1 & 2 in Heliosheath
Dave McComas: 8
Mollweide all-sky projection showing locations of Voyagers
Voyagers provide detailed information in these two directions
Dave McComas: 9
Dave McComas: 10
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
Dave McComas: 11
McComas et al., Science 2009
Dave McComas: 12
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
Dave McComas: 13
The Start of a New Paradigm
McComas et al., Science 2009
Dave McComas: 14
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
Dave McComas: 15
Circularity of the IBEX ribbon
Funsten et al., ApJ, 2013
Dave McComas: 16
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
Dave McComas: 17
6 of 13 Proposed Ribbon Sources
McComas et al., JGR 2010+7 others…
Dave McComas: 18
More New Ribbon Ideas Emerge
Dave McComas: 19
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.
Dave McComas: 20
Dave McComas: 21
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
Dave McComas: 22
Latitude-Dependant & Direct Ribbon Source
McComas et al., ApJS, 2012
Dave McComas: 23
Spatial Retention of Ions & the IBEX Ribbon
Schwadron and McComas, ApJ, 2013
Simulation IBEX Data
Dave McComas: 24
Additional Detailed Mechanisms
Dave McComas: 25
Spectral Slopes of ENAs
McComas et al., Science 2009
Dave McComas: 26
Pickup Ions k Distributions
Dave McComas: 27
Livadiotis et al. ApJ, 2013
Pressure of the proton plasma in inner heliosheath
Dave McComas: 28
Zirnstein et al. ApJL, 2014
Multi-component nature of the inner and outer
heliosheath plasma and its effect on ENA flux
Dave McComas: 29
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
Dave McComas: 30
Ribbon/GDF Separation
Dave McComas: 31
Flow Away from Pressure Max
Dave McComas: 32
Heliotail
Dave McComas: 33
Dave McComas: 34
McComas et al. ApJ, 2013
The heliotail revealed by IBEX
Dave McComas: 35
Tail Structured by Slow/Fast SW
Starboard
looking
downtail
Port
looking
downtail
E-folding losses
(cooling length)
~100-200 AU
Dave McComas: 36
Local IS Field Twists Heliotail
Dave McComas: 37
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
Dave McComas: 38
LISM Interaction – Alfven Wings?
Dave McComas: 39
5 Years of IBEX Data
Dave McComas: 40
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
Dave McComas: 41
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
Dave McComas: 42
Leveling Off of ENA Fluxes
• Heliotail fluxes
continue to drop owing
to greater distance and
longer “recycling” time
for SW ions
Dave McComas: 43
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 %
Dave McComas: 44
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
Dave McComas: 45
Recycled Solar Wind
Dave McComas: 46
Ribbon Changes by Region
Dave McComas: 47
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
Dave McComas: 48
Motions of Sun and Local Clouds
Dave McComas: 49
IBEX ISN Observations
Möbius et al., Science 2009
Dave McComas: 50
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]
Dave McComas: 51
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
Dave McComas: 52
McComas et al., Science, 2012
Dave McComas: 53
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
Dave McComas: 54
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
Dave McComas: 55
Leonard et al., 2015 (submitted)
• Lee et al. [2012] analytic model
not good for S/C pointing out of
ecliptic
• In ecliptic consistent values
Dave McComas: 56
Ecliptic Pointing Flow Vectors Converge
McComas et al. [2012] tube still
consistent
McComas et al., ApJ 2015
Dave McComas: 57
…But Requires Much Warmer ISM
Old Ulysses Value
He now isothermal with
O/Ne
McComas et al., ApJ 2015
Dave McComas: 58
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
Dave McComas: 59
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
Dave McComas: 60
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!!!
Dave McComas: 61
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
Dave McComas: 62
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
Dave McComas: 63
First: Plasma Sheet Images
Orbit 52
McComas et al., JGR 2011
Orbit 51
Dave McComas: 64
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
Dave McComas: 65
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