EuroPlanet, Sept. 22, 2006Stas Barabash, Page 1 ENA diagnostics of the solar wind interaction with...

EuroPlanet, Sept. 22, 2006

Stas Barabash,

ENA diagnostics of

the solar wind interaction with

planetary bodies

Stas BarabashSwedish Institute of Space Physics (IRF), Kiruna, Sweden


Stas Barabash,

Outline

ENA introduction

Sci. objectives of planetary ENA imaging. What can one achieve by ENA imaging?• Global ion distribution inside magnetospheres: Mercury, Earth• Plasma distributions in the interaction region: Mars, Venus, MEX data• Outflowing planetary ions: Mars• Global neutral gas / dust distribution: Europe, Phobos torus, Saturn rings• Surface interaction. Sputtered ENAs. Precipitation maps: Mercury, Moon• Atmosphere interaction. Backscattered ENAs. Precipitation maps: Mars,

MEX data• Global dynamics: Mercury, Earth

Conclusion• Planetary ENA experiments• New frontiers for planetary ENA imaging


Stas Barabash,

Planetary ENA experiments (out side the Earth)

Planet Mission / Instrument Remark

Mars Mars Express, 2003

ASPERA-3

100 eV - few keV

Venus Venus Express, 2005

ASPERA-4

100 eV - few keV

Jupiter Cassini, 1997/INCA

Voyager

E > 20 keV

Non-ENA dedicated (Kirsch et al., 1981)

Saturn Cassini, 1997/INCA

Voyager

E > 20 keV

Non-ENA dedicated (Kirsch et al., 1981)

Moon Chandrayaan-1, 2008

SARA

10 eV - 3 keV

Sputtering and backscattered ENAs

Mercury Bepi Colombo, 2013

MPO / SELENA

MMO / ENA

Shutter techn. 20 eV - 1.5 keVReplica of SARA


Stas Barabash,

ENA introduction (1)

• No gravitation banding: E >> Eescape, i.e., Eescape (O) = 2.4 eV for Mars

• Processes resulting in ENA production in planetary environments• Neutralization: charge - exchange on neutral gas and dust• Surface (upper atmosphere) interaction: backscattering, sputtering, and

recoil

B0

A+

A0

neutral gas

A+

A0

dust

A+ A0

surface /atmosphere

A+ B0

surface (B) /atmosphere

Ion neutralization

Surface / atmosphere interaction A+ C0

surface (B) /atmosphere


Stas Barabash,

ENA introduction (2)

• ENAs propagate as photons: imaging of populations resulting in ENAs

• Neutralization (CX):

• Advantages: Provides ion or neutral gas (dust) global distribution • Drawback: line-of-sigh integrals => inversion problem, extra assumptions

• Surface interaction:

• Advantages: Provides the integral flux at the surface (cm-2 s-1 eV-1), no inversion. Surface (upper atmosphre) works a display

• Drawback: Loss spectral information

€

jena ~ σ jionn dl∫

€

jena ~ Fion (Eb ) surface f (θ) g(E,Eb )


Stas Barabash,

ENA introduction. Non magnetized planets (3)

• Direct interaction with the upper atmosphere/ionosphere: Venus/Mars. ENA diagnostic to reveal:

• Morphology of the interaction region• Global dynamics of the interaction region• Precipitation onto the upper atmosphere (backscattering)

• Direct interaction with the surface: Moon. ENA diagnostic to reveal:• Morphology of the interaction region• Space weather effects


Stas Barabash,

DIAGNOSTIC OF

THE INTERACTION REGION MORPHOLOGY (MARS/VENUS)


Stas Barabash,

ENAs at Mars


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Shocked SW ENAs. NPI observations


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NPI ENA observations vs. simulations

ENA signal


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Inversion results

// Solar wind parameters (non-fitted)

pars[0] = 2.5; // Solar wind proton density [#/cm^3]

pars[1] = 400e3; // Solar wind speed [m/s]

pars[2] = 10; // Solar wind temperature [eV]

// Geometry parameters (fiitted)

pars[3] = 0.1667; // alpha, magnetopause penetration

pars[4] = 0.55; // x_0, Bow shock position [Rm]

pars[5] = 1.35; // x_nose, magnetopause position [Rm]


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Futaana, et al, 2006


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Subsolar jet (cone)

Futaana, et al, 2006


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Non-observation of O-ENAs

• Oxygen ENAs have NOT been observed by ASPERA-3: fluxes below the instrument limit (2.5·104 cm-2 sr-1 s-1) Galli et al.,. 2006).

• Scaling the escape rate gives Q(O+) < 1023 s-1. In agreement with the direct escape measurements.


Stas Barabash,

GLOBAL DYNAMICS


Stas Barabash,

Response to an interplanetary shock (1)

Futaana, Barabash et al., 2006


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ENA jet oscillations

T

Oscillation periods: 50 and 300 sec

Depth ~20-30%

Grigoriev et al., Space Science Rev.,, 2006


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Diagnostic of the dynamics

• Time scale of the interaction region reconfiguration against interplanetary disturbances.

• Time scale of the local instabilities at the induced magnetospehere boundary / plasma oscillations in the magnetospheath.


Stas Barabash,

DIAGNOSTIC OF THE

PLASMA PRECIPITATION


Stas Barabash,

Backscattering ENAs. Simulations (1)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

• Monte Carlo simulation of proton / ENA backscattering (Kallio and Barabash, 2000)


Stas Barabash,

Backscattering ENAs. Simulations (2)

• Backscattering hydrogen velocity distribution (Kallio and Barabash, 2000)• Albedo ~60%, Energy loss ~40%




Stas Barabash,

Backscattering H-ENAs. ENA albedo

Backscattered hydrogen (ENA albedo)

• Precipitating particles (ENAs and protons) experience elastic and non-elastic (CX, excitation) collisions with the upper atmosphere gases (mostly O and CO2)

• Kallio and Barabash (2001) predicted backscattering H atoms caused by hydrogen ENA precipitation onto the upper atmosphere.

• ENA energy ≈ 0.6 x precipitating energy

• ENA albedo ≈ 0.6


Stas Barabash,

Backscattering H-ENAs. Observations (1)

Backscattering H-ENAs

H-ENAs from subsolar region


Stas Barabash,

• H atom Energy:

Subsolar ENAs: 2.14 keV

Backscattering: 1.36 keV• Compare with ~2 keV shocked solar

wind as measured by IMA in the magnetosheath

• Flux: (8 - 14)·106 cm-2 sr-1 s-1

Backscattering H-ENAs. Observations (2)

160 ns

200 ns Backscattering H-ENAs. ENA albedo

H-ENAs from subsolar region. ENA jet

27 Feb. 1948 - 1958

TOF, ns


Stas Barabash,

Backscattering H-ENAs. Precipitation maps

• Backscattered ENAs flux is proportional to the precipitation flux and can be used to construct precipitation maps

NPD FoV longitude - latitude coverage. Orbit 500. July 11 1840 - 1900

Precipitation map NPD1 - Dir0. Orbit 500. July 11 1840 - 1900


Stas Barabash,

DIAGNOSTIC OF

THE INTERACTION REGION MORPHOLOGY (THE MOON)


Stas Barabash,


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Sputtered atoms

(Johnson and Baragiola, 1991)


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Minimagnetosphere (Lin et., 1998)


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Imaging magnetic anomalies

Orbit motion

FoV (channels)


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Sputtered atoms

• Angular distribution does not depend on the impinging ion flux angular distribution (statistically).

• Atoms are not affected by electromagnetic forces and gravitation (E >> Eescape = 1.7 eV for Fe).

• Sputtered atoms: O, Na, Al, Si, K, Ca, Ti, Mn, Fe• Atom sputtering conserves stoichiometry - an analytical tool in the lab.• Thomson - Siegmund spectrum:

€

f ~E

(E + Ebind)3(1−

E + EbindEcut−off

),

Ecut−off = 4E ion M1 + M2( )

M1M2( )2

f ~ 1E2 for E >> Ebind and E << Ecut−off


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Stas Barabash,

DIAGNOSTIC OF SPACE WEATHERING (THE MOON)


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Space weathering

• Space weathering: changing albedo (visible, IR) under space environment effects, e.g., particle and photon flux, mmicrometeor bombardment

• Swirl - like albedo marking in Crisium impact basin antipodal region (Reiner Gamma region, Lin et al., 1988, Hood et al. 1999)


Stas Barabash,

ENA emissions at Mars: simulations and observations on Mars Express

Stas Barabash and Mats Holmström

Swedish Institute of Space Physics, Kiruna, Sweden


Stas Barabash,

ENA production at Mars

• Charge - exchange on the exosphere (extended due to low gravity!) • Upstream solar wind• Shocked solar wind• Planetary oxygen ions

• Backscattering of the solar wind protons


Stas Barabash,

CX SW ENAs. Simulations (1)

Highest neutral gas density

Plasma distribution?

Bow shock

The boundary

CX: undisturbed solar wind on the extended exosphere

CX: shocked solar wind on the exosphere

SW void

SW void

Mars

Solar wind

• Typical morphology: neutral solar wind, ENA fluxes tangential to flow lines


Stas Barabash,

CX SW ENAs. Simulations (2)

• Holmström et al., 2002


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CX oxygen ENAs. Simulations (1)

• Oxygen ion distribution (Test partciles in the empirical model, Kallio, 1997; Barabash et al., 2002)




Stas Barabash,

CX oxygen ENAs. Simulations (2)

• O - ENA fluxes 0.1 - 1.65 keV (Barabash et al., 2002)• Typical morphology: subsolar jet and tailward flux


Stas Barabash,

MEX ENA sensors

The instrument performance (NPI, NPD)

NPI NPD

Energy range, keV ≈0.1 - 60 0.1 - 10

Energy resolution, E/E No 0.8

Mas s resolution, No H, O

Intrinsi c fie ldo f view 9° × 344° 9° × 180°

Angular resolution 4.6° × 11.5° 5° × 40°

G-fac /torpixel

(ε no t included), cm2sr

2.5 × 10-3 6.2 × 10-3

Efficiency 0.1 - 1% 1 – 15%

NPD

NPI


Stas Barabash,

MEX ENA observations

• Global structure of the solar wind interaction region• Shape of the solar wind void (NPI, Herbert Gunell et al., 2005)• Subsolar ENA jet (NPD, Futaana et al., 2005)• Oscillations of the ENA jet (NPD, Futaana et al., 2005)

• Solar wind - atmosphere interaction• Occultation of the neutral solar wind at Mars (NPI, Klas Brinkfeld et al.,

2005) • Solar wind proton precipitation onto the atmosphere: ENA albedo

(backscattered ENAs) (NPD, Futaana et al., 2005)

• Oxygen ENAs are not yet identified in the available data.


Stas Barabash,

Ion distributions inside magnetospheres. Pretty ENA images

Earth’s ring current, outer vantage pointIMAGE / HENA, courtesy D. Mitchell, APL

Earth’s ring current, low altitude polar vantage pointAstrid-1 / PIPPI, Barabash et al., 1999

Earth’s ring current, from belowAstrid-1 / PIPPI, C:son Brand et al., 2001

Mercury magnetosphere, 30 keV protons, polor vantage point, Simulations, Barabash et al., 2001


Stas Barabash,

Ion distributions inside magnetospheres. Science

• Ring current physics• Dynamics• Global morphology during

different conditions• Composition (H, He, O)

variations• Storm / substorm relations• Ion dynamics during substorms

injections• Plasma sheet depolarization• M - I coupling (from deduced ion

distribution)• Microphysics though P/A

distribution reconstruction. Yet, it requires high angular resolution

QuickTime™ and aGIF decompressor


IMAGE / HENA Movie, courtesy Pontus C:son Brandt, APL


Stas Barabash,

Plasma distributions in the interaction region

• ENA imaging non-magnetized planets, Mars and Venus.• Simulations by Kallio et al., 1998; Holmström et at, 2002; Mura et al., 2002;

Lammer et al., 2002; Gunell et al., 2004.• The main scientific objective: determined the structure of the interaction

region

ENA detectorENA

ENA


Stas Barabash,

Plasma distributions in the interaction region. Mars

• Simulations by Holmström et al., 2002


Stas Barabash,

Plasma distributions in the interaction region. Venus

• Simulations by Gunell et al., 2004


Stas Barabash,

ENA Occultation at Mars (1)

vMars

Photon flux

Solar wind / ENA flux

~ 4°

0 1 2 3 4 5 6 7 x107

Simulated ENA flux at SZA=160°

Holmström et al [2001]

Interaction with the upper atmosphere - scattering


Stas Barabash,

ENA Occultation at Mars (2)

Scatteredphotons ENA

Backgroundnoise

S/C in Mars umbra

S/C in Marspenumbra

40

Sector 21

Observed flux 2·105 cm-2 s-1 is consistent with 0.3% of the solar wind flux


Stas Barabash,

Imaging outflowing planetary ions

• Planetary ions escaping the non-magnetic atmospheric bodies (Mars, Venus, comets) charge - exchange with the exospheric neutrals and are converted to ENAs.

• O-ENAs images visualize the instantaneous distribution of O+ ions.• ENA imaging is the most promising way to determine the total escape rate, the key

number for understanding solar wind effects on the atmospheric evolution. In-situ measurements require assumptions on global distributions.

• O- ENA imaging is being attempted on Mars Express / ASPERA-3.


Stas Barabash,

Neutral gas distribution (1). Europa torus

• Neutral gas immersed in the background of charged particles shines in ENAs.

• Mauk et al., 2003 observed the Europa torus around Jupiter in ENAs (Cassini/INCA).

• Main finding: Europa gas cloud (most probable from ice sputtering) is comparable with the one from the volcanic moon Io.

• The Titan exosphere immersed inside the Saturn radiation belts is also shining in ENAs (simulations by Dandouras and Amsif, 1999 in preparation for the Cassini / INCA experiment).

Raw image

Point source (calibration)

Deconvolved image

Europa torus

Jupiter


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Neutral gas distribution (2). Phobos torus

• Weakly outgassing (mostly water, Q~1023 s-1) Phobos results in a torus immersed in the solar wind flowing around Mars. The torus is a possible source of low energy ( < 1 keV) ENAs (Mura et al., 2001).

• Mars Express / ASPERA-3 will attempt imaging to constrain the outgassing rate and obtain the radial profile.

Only Mars exosphere Only Phobos torus

Mars + Phobos

Obstacle


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Ion / dust neutralization. Saturn radiation belts / rings

• Mauk et al., 1998. Simulations of ENA signal from F-ring of Saturn in the frame Cassini / INCA experiment.

• F - ring looks like a circular line source.• Science:

• Trapped ion radial diffusion rate• Particle size constraining from energy

spectrum• Efficiency of ion / ring interactions

H+

H0 , ~ 50 keV, > 50%

dust particle ~0.5 m


Stas Barabash,

Surface interaction. Sputtered / Backscattered ENA

• Energy spectrum follows the Thompson - Sigmund formula:

• Typical fluxes (input flux dependent, integrate within 10% energy band, 10 - 100 eV): 103 - 104 cm-2 s-1 sr-1

• Mass composition reflects the surface elemental composition. For Mercury: O, Na, K, Ca, Mg, Al, Si

• Precipitating ions (H+) can be also backscattered as H-ENAs.• Sputtered / backscattered ENA imaging reveals:

• Precipitation maps similarly to auroral display (ENA - “aurora”)• Inputs to surface - bound exospheres (Mercury, Moon)

€

f ~E

(E + Ebind)3(1−

E + EbindEbeam

), f ~ 1E2 for E >> Ebind and E << Ebeam

Na image by Potter and Morgan, 1990.

Hot spots: precipitation regions or minerological feature?


Stas Barabash,

Surface interaction. ENA - aurora on Mercury

Ion precipitation maps

Sputtered Na - ENA images (10 - 40 eV)

H+, solar wind H+, Tail source, 30keV Na+, photoions


Stas Barabash,

Surface interaction. Minimagnetospshres on the Moon

• The Moon surface is exposed to the

solar wind flux except areas of strong

remanent magnetic fields,

minimagnetopsheres (Lin et al., 1998).

• The minimagnetospheres will be

“visible” on sputtered / backscattered

ENA images as voids.

• ENA imaging is the only technique

capable of visualizing

minimagnetospsheres.

• Simulations by Futaana, Barabash, and

Holmström, 2004 for a void of 100 km

diameter and a virtual ENA detector at

100 km height.


Stas Barabash,

Atmosphere interaction. Backscattering H-ENAs

Backscattered hydrogen (ENA albedo)

Precipitating protons

and ENA from SW

• Kallio and Barabash (2001) predicted backscattering H atoms caused by hydrogen ENA and solar wind proton precipitation onto the upper atmosphere of Mars (at Venus the similar process operates).

• Ebs/Ensw ≈ 0.6

• Fbs/Fnsw ≈ 0.6


Stas Barabash,

Atmosphere interaction. Mars Express results

Subsolar point

NPD1 FoVNPD2 FoV


Stas Barabash,

• H atom Energy: 1.69 - 2.14 keV (160 - 180 ns) • Compare with ~2 keV shocked solar wind as measured by

IMA in the magnetosheath• Flux: (8 - 14)·106 cm-2 sr-1 s-1

• Only direct precipitation of the solar wind down to the exobase altitude (250 km) can be accounted for such high fluxes! In agreement with IMA ion observations of the deep solar wind penetration.

• Stong energy and momentum deposition to the upper atmosphere.

Atmosphere interaction. Mars Express results

160 ns

180 ns


Stas Barabash,

Global dynamics. Dst and total ENA production

• ENA flux at a vantage point is a function of the global ion (neutral gas) contain => global dynamics of the system.

• Jorgensen et al., 1997 POLAR / IPS observations (17.5 …~ 100 keV)

• ENA signal time variation follows moderate storm dynamics.

• The characteristic time scales can be determined from a single point ENA measurements.

• Jorgensen et al., 2001 also reported short-lived ENA bursts associated with substorm signatures

Dst index and

POLAR ENA signal

Recovery phase

Main phase


Stas Barabash,

Global dynamics (2). Fine time variations

• Ebihara, Barabash, Ejiri, 1999. Simulation of total ENA production

• ENA production for E < 30 keV follows Dst quite precisely

• High energy ENA variations reflect particle motion in the inner magnetosphere

Variations with drift angular frequency (~1 hour) and beatings caused by finite energy window


Stas Barabash,

Global dynamics. Application to Mercury

• Problem of distinguishing spatial and temporal variations in compact magnetospheres (small size, short reconfiguration time): necessity of global techniques.

• Mercury case: substorm time ~1 min, one substorm per 5 min (Siscoe et at., 1975)

• ENA signal profile is a sequence of flashes lasting for ~ 1min each.• For studies of global dynamics the details of the generation mechanisms are

not important.

Time

EN

A s

ign

alin

ten

sity

How often? 5 min?

How long is recovery?How fast is injection?

How long? 1 min?


Stas Barabash,

New frontiers for planetary ENA imaging

Priorities for new investigations and

new experimental challenges

• Earth• High angular resolution (~1° x 1° / pixel) for all energy ranges: pitch -

angle effects and microphysics • Non-atmospheric bodies (Mercury, Moon, asteroids)

• ENA imaging mass spectroscopy (M/M ~ 20…40): surface - plasma interactions

• Non-magnetic atmospheric bodies (Mars, Venus, comets)• Low energy ENA imaging (tens eV) with moderate mass resolution:

escape processes

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