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Energetic Neutral Atom Imaging of the Ganymede - Jovian Magnetosphere Interaction S. Barabash 1 , Y. Futaana 1 , M. Wieser 1 , X. Jia 2 , P. Wurz 3 , P. Brandt 4 , K. Asamura 5 1 Swedish Institute of Space Physics, Kiruna, Sweden - PowerPoint PPT Presentation
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Energetic Neutral Atom Imaging of the Ganymede - Jovian Magnetosphere Interaction
S. Barabash1, Y. Futaana1, M. Wieser1, X. Jia2 , P. Wurz3, P. Brandt4, K. Asamura5 1Swedish Institute of Space Physics, Kiruna, Sweden
2Dept. of Atmospheric, Oceanic, and Space Science, U. of Michigan, Ann Arbor, USA3 University of Bern, Physikalisches Institut, Bern, Switzerland
4Applied Physics Laboratory, Johns Hopkins University, Laurel, USA5Institute of Space and Astronautical Science,Sagamihara, Japan
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Energetic neutral atom imaging of Ganymede will be performed:Particle Environment Package (PEP), a particle sensor suite including an
ENA imager, was selected to fly onboard JUICE
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PEP configuration (baseline)
• 6 sensors selected (Core configuration)
• 3 units• Combines first-ever at Jupiter
energetic neutral atom imaging with in-situ 3D plasma measurements
• Performs first-ever high resolution gas mass spectroscopy at icy moons to identify surface constituents
• JNA: Jovian Neutrals Analyzer
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ENA imaging concept
• Energetic Neutral Atoms (ENAs) propagate unaffected by electromagnetic forces
• For E >> Eesc (0.64 eV, oxygen) the gravitation bending of trajectories is negligible
• ENA can be used for remote diagnostic of the region of the origin
• Relevant sources:• Backscattering of precipitating ions• Sputtering of the Ganymede surface
materials• ENA flux
A+ A0
surface
A+ B0
surface (B)
€
jena ~ Fion (Eb ) surface f (θ) g(E,Eb )
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ENA imaging of the Moon. Chandrayaan-1 results
• Chandrayaan-1/SARA experiment showed that imaging backscattered ENAs is a new and powerful diagnostic tool to investigate plasma - surface interactions
• High backscattered hydrogen flux (20% vs. < 1% expected)
• Mini-magnetospheres screening-off a fraction of the solar wind is well visible on ENA images
Magnetic anomaly
ENA relative flux
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ENA production at Ganymede
• Focus on plasma - surface interaction: charge - exchange ENAs are only relevant for global imaging
• Plasma at the surface• Co-rotating plasma precipitating
along open field lines• Energetic particles from the rad. belts
• Two main mechanisms to produce ENAs• Backscattering (H, O, S) • Sputtering (mostly H and O)
• Imaging of the precipitating plasma via ENAs• Geometry of the precipitation regions:
open/closed field line region• Dynamics of the precipitation• Correlation with albedo features
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H+
S3+
S+
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Sputtered ENAs (1)
Sputtered yields are very high (> 10) for
heavy projectiles on water ices
(Baragiola et al., 2003)
BUT
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1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1 10 100 1000 10000
Energy, eV
Norm. spectrum
30 keV H -> O, Eb=3.4 eV
30 keV H-> O, Eb= 1 meV
Sputtered ENAs (2)
• Spectrum of the sputtered ENA is: Thomson - Siegmund (pure metal) but with very low very binding energy (Shematovich, private communication)
• Estimations of the fluxes are difficult
€
f ion ≈102cm−2s−1sr−1ev−1 at 10 keV
ΔE ≈ 3 keV
Yield ≈10 for heavy
Fneutrals ≈ Yeild f ion ΔE
2π ≈ 3⋅106cm−2s−1sr−1
Fneutralsmeasurable (E >10eV ) ≈ P Fneutrals
P < ≈10−2
Fneutralsmeasurable (E >10eV ) <≈ 3⋅104 cm−2s−1sr−1
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Laboratory experiment on particle irradiation of ice (1)
• To understand the sputtering and backscattering processes dedicated ice experiments on particle irradiation of H2O ices were conducted using a PEP / JNA prototype at the ion facilities at U. of Bern
Ice block
ENA sensor
Ion beam
Backscattering ENA
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Laboratory experiment on particle irradiation of ice (2)
• Typical conditions:• “Dirty” water ice T= 150 K• Pressure 10-5 mbar
• ø5mm beams H+ and O+• Energy range from 1 keV to 43 keV• Masses analyzed: H, O, and “heavy”
neutrals • ENA spectra in 9 energy bands centered at
from 10 eV to 2560 eV
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H+ beams
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Backscattering
Sputtering
Sputtering
No corrections for energy - dependent sensitivity
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O+ beams
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No corrections for energy - dependent sensitivity
Recolled H
Sputtered
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Summary of the results
• Backscattered H-ENA spectrum (1 keV H+) is Maxwellian (T=290 eV). Similar to the regolith but T is 2-3 times higher.
• Sputtered H-ENA spectrum (33 keV O+) is different from both Maxwellian and Thompson-Siegmuind. Cut-off at 2-3 keV much lowers than predicted 8 keV.
• The backscattered coefficient 27% (similar to 19% observed from the Moon)
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ENA imaging of Ganymede (1)
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Plasma precipitation regions
Jia et al., 2011, MHD - model
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ENA imaging of Ganymede (2)
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Relevance of the ENA imaging from an orbiter for lander
• ENA imaging from an orbiter (JUICE):• Provide remote diagnostic of the plasma (ion) environment at the
lander surface• Temporal variations and correlations with the surface properties
variations measured locally at the lander• Define energy and particle inputs (fluences) to the local areas around
the lander