The induced magnetosphere of Venus
as seen by ASPERA-4 and MAG on
Venus Express
Gabriella Stenberg Wieser
Swedish Institute of Space Physics
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The planet Venus
named after the Roman Goddess of love and beauty
 Distance to Sun: 0.72 AU
 Radius: 6052 km
 Mass: 4.8676 × 1024 kg
 Surface temperature: 735 K
 Atmosphere: CO2 (96.5%), N, SO2, Ar
 Cloudy
 Surface pressure: 9.2 MPa (92 bar)
 Orbital period: 225 days
 Sidereal rotation period: 243 days
 No intrinsic magnetic field
https://en.wikipedia.org/wiki/Venus
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Induced magnetospheres
 No intrinsic
magnetic field
Earth
Venus
 Solar wind interacts
directly with the
upper atmospheres
 The interplanetary
magnetic field
determines the
polarity
Mars
 Interaction region is
small compared to
Earth
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The disappearing magnetic barrier
Zhang et al., 2009
 The interplanetary magnetic field (IMF) determines the magnetic
configuration of the magnetosphere
 When the IMF is parallel to the Sun-Venus line the magnetic
barrier disappears
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Ion escape
Heavy ions (m/q≥8): 5x1024 s-1
H+:
14x1024 s-1
Nordström et al., 2013
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Escape topology
Energy
Energy
YVSE, Rv
Flux
Flux
Barabash et al., Nature 2007
 Difference between +E/-E hemispheres
 Escape larger in the plasma sheet
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Tail asymmetries
Zhang et al., GRL 2010
 Magnetic field draping is different
in +E/-E hemispheres
 The average magnetic field is
irregular in the –E-hemisphere
 Also seen in particle
density/velocity
Rong et al., JGR 2014
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Escape processes
Dubinin et al., 2013
 Acceleration by the slingshot effect
 Other mechanisms: pickup, ambipolar diffusion, waveparticle interaction, reconnection
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Reconnection
Zhang et al., 2012
 Flux rope plasmoid observed
 Enhanced particle fluxes seen
at the same time
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Space weather effects
Heavy ion escape increases a factor 1.9 during CIR/CMEs
51% of the escape during 35% of the time
Edberg et al., 2011
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First ENA observations at Venus
 Narrow tailward
stream coming from the
dayside exosphere
 Shocked solar wind
protons charge-exchange
with the neutral
hydrogen exosphere
 No oxygen ENAs
observed
Galli et al., 2008
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Precipitation
He2+
He+
He
He
He
He2+
U-238
U-235 He-4
Th-232
He
He2+
He
He
He2+
He+
He
He
1x1021 s-1
Fedorov et al., 2008
Stenberg Wieser et al., 2015
He+
He
8x1022 s-1
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Hot Flow Anomalies
 Explosive phenomenon:
occurs when a
discontinuity in the IMF
interacts with the bow
shock
 A pocket of reflected
solar wind plasma is
heated and expands
 Indications of HFA at
Venus first observed on
the MESSENGER flyby
(Slavin et al., 2009)
Collinson et al., 2012
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Hot Flow
Anomalies
 Depleted and
noisy magnetic field
 Core of rarified
hot plasma
 Compressed
plasma and peaks
in B around the
core
 Deflection of solar
wind flow
Collinson et al., 2014
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Waves
 Proton cyclotron waves:
revealing pickup ions far
upstream (Delva et al., 2008)
 Whistler waves: a sign of
lightning? (Russell et al., 2007)
 Mirror mode waves:
compressional waves in solar
wind and magnetosheath
(Volwerk et al., 2008)
 Large-amplitude non-linear
waves: Kelvin-Helmholtz
generated? (Walker et al., 2011)
 Waves upstream of bowshock
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ASPERA-4
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