Structure and dynamics of induced plasma tailsCésar L. Bertucci Presented by Oleg VaisbergInstitute for Astronomy and Space Physics, Buenos Aires, [email protected]
The Third Moscow Solar System Symposium 3M-S3 Space Research Institute, Moscow, Russia, October 8-12, 2012
Introduction• Downstream counterpart of IM
formed by ‘accreted’ frozen in fields (Alfven, 1957)
• In principle B and V dictate basic geometry (not always so simple!)
• Current systems sustain tail structure.
• Spatial place where local plasma tries to be ‘assimilated’ (return to equilibrium if that exists!) by the external flow acceleration.
• Local plasma acceleration involves current-field forces and non MHD processes.
Afte
r Sau
nder
s an
d R
usse
ll, 1
986 B
V Ec = - V x B
Dubinin et al., 2006
Mars
Outline
• Tail morphology– Magnetic field topology (magnetotail).– Plasma regions.
• Energetics and dynamics• Conclusions• Outstanding questions
Magnetic morphology
Venus magnetotail• Venera: Tail boundary topologically
connected to dayside IMB (Vaisberg and Zelenyi, 1984).
• PVO: IMB well defined up to 12 RV is rotational discontinuity (Saunders and Russell,1986).
• Far tail cross section (5-12 RV) elongated along B.
• Cross tail field PVO: B= 2 to 4nT and more
predominant on north (outward Ec) hemisphere possible trans terminator flow asymmetry.
VEX: 1.3>R>3 RV: depends on nominal Ec (Zhang et al., 2010). B asymmetry.
Ec
Saunders and Russell, 1986
VEX MAGZhang et al., 2010
N= 48
-10RV > XVSO >-12RV
+B’x-B’x
B
IMB = 50%
N = 70
B
Mars’ magnetotail
Yeroshenko et al., 1990
Rosenbauer et al., 1994 • Short and mid range magnetotail field geometry depends on IMF clock angle (Yeroshenko et al., 1990, Schwingenschuh et al., 1992, Crider et al., 2004).
• Solar wind pressure dependence.– Lobe PMAG (Rosenbauer et al.,
1994).
– Flaring angle (Zhang et al., 1994)
• Short-range magnetotail flares out from the Mars–Sun direction by 21◦ (Crider et al., 2004).
Zhang et al., 1994
Average 13o
B
Titan’s magnetotail: variability sources
Kronian field stretch @ Titan orbitSouthern summer
Apart from the MP proximity and SLT effect... Titan’s distance to Saturn disk changes seasonally...
and during a planetary period ...
So, every ~10.8 hours all this happens....
Titan’s orbit10.8 h
Bertucci, 2009
Ber
tucc
i, et
al.,
200
9
1
3
after Khurana et al., 2009
2
4
Titan’s magnetotail: magnetic structure
Backes et al., 2005
TA flyby (1.4 RT distance)
T9 flyby (~5 RT distance)
Tail lobe fields and polarity reversal are compatible with upstream V-B geometry (e.g. Neubauer et al., 1984, 2006, Bertucci et al., 2007).
V Departure from nominal flow as much as 40° (Bertucci et al., 2007, Szego et al., 2007, McAndrews et al., 2009).
North Lobe
South Lobe
Tail
Plasma morphology
Plasma morphology - Venus• Pre VEX observations postulated inner
and outer mantles and a neutral sheet.
• Inside IMB, planetary ions including H+, He+, O+, and O2+ (Fedorov et al., 2008, 2011)
• Energy of planetary H+ is high (several keV) at the boundary layer and decreases towards the neutral sheet.
• Energy of heavy planetary ions behaves similarly. Thin layer of 500–1000 eV heavy ions in neutral sheet.
• H+ and He+ ions create an envelope around plasma sheet.
• Also at Mars and Titan: Tail photoelectrons not confined to ionosphere (Coates et al., 2010).
Fedorov et al., (2008), see also Fedorov et al., 2011
H+ flux E> 300 eV
m/q=14 flux E> 300 eV
VEX (Solar Min)
Pre-VEX
Phillips and McComas (1986)
Plasma morphology - Mars
• Planetary heavy ions (O+ and O2+) inside IMB (Lundin et al., 2004).
• Ion energy decreases from IMB down to plasma sheet (Fedorov et al., 2006)
• 1-keV energy heavy ions populate the neutral sheet (Fedorov et al., 2008).
• Planetary, low energy ions (H+ and higher masses) also observed and dominate plasma escape (Lundin et al., 2009)
Fedorov et al., 2008
Heavies M/Q >14
M/q =1-2 flux E/q> 300 eV
M/q>14 fluxE/q > 300 eV
Fedorov et al., 2006
Ec
Plasma morphology - Titan• Cold, dense ionospheric
plasma inside the induced magnetosphere.
• Tail shows a ‘split’ signature– 1) Ionospheric photoelectrons
Heavy (16-19,28-40 amu) field aligned ions (Szego et al., 2007).
– 2) colder electrons and light (2 amu) ions.
• ne>5 cm-3 maps show still ambiguous role of Ec in the distribution, but influence is expected (Modolo, Bertucci et al., 2012 in prep).
T9 flyby
Modolo et al., 2012, in preparation
Bertucci,et al.,,Coates, et al., 2007
1 2
n > 5 cm-3
Ec
Flow
Flow Tail
Energetics and dynamics
Venus• PVO: From average magnetic tail
configuration plasma parameters are obtained (McComas et al.,1986).– vx, ax (using also E// continuity)– ax is used with MHD momentum
eq. to calculate n and T
• Evidence of acceleration compatible with JxB force (Fedorov et al., 2008).
• Substorm-type tail reconfiguration
(Volwerk et al., 2009, Zhang et al., 2011).
PVO, B derived plasma properties(McComas et al., 1986)
xO
xO
Z
Y
Fedorov et al., 2008
Mars• Plasma sheet (2.8 RM)
– Ion energy in the plasma sheet is similar to that of solar wind H+ (Dubinin et al., 1993).
– E/q of ions does not depend on M/q. E/q also coincides with peak energy of singles Electrostatic field.
– JxB ambipolar field seems to explain acceleration in neutral sheet.
• Boundary layer (near IMB < 2RM)– O+ and O2+ energy show linear
increase with distance. – Gained energy compatible with of
convective electric field.• Evidence of near tail reconnection
Eastwood et al., (2008)• Intermittent detachment of planet-
ary plasma (Brain et al., 2010)
Dubinin et al., 1993
Plasma sheet
Ion extraction by Ec penetration in BL
Dubinin et al (2006)
Titan• Mid range tail observations near
IMB display field-aligned fluxes of photoelectrons.
• At the same time, ion fluxes of several tens of eV.
• Mid range tail ion observations are consistent with ambipolar electric field acceleration along flield lines coming from the dayside (Coates, et al., Szego, et al., 2007).
• Event 2 is dominated by mass 2 ions with energies of 100 eV. Not explained yet.
Ions
B polarity reversal layer
Tail
Electrons
DAYSIDE
Conclusions and outstanding questions• The geometry of the magnetotails of Mars, Venus and
Titan are dominated by the orientation of the upstream magnetic field and the upstream flow velocity vector.
• The magnetotail = induced magnetosphere is almost exclusively populated by planetary particles.
• Although with different sizes, the spatial plasma distribution within the tails of Mars and Venus is similar with a few exceptions. Titan displays reccurring split signatures.
• Mars’ mid and long-range magnetotail is poorly known.• Wider plasma species and magnetic field survey of
Titan’s tail needs to be carried out in order to begin a discussion of their dynamics.
