Structure and dynamics of induced plasma tails

1. Structure and dynamics of induced plasma tails César L. Bertucci Presented by Oleg Vaisberg Institute for Astronomy and Space Physics, Buenos Aires, Argentina cbertucci@iafe.uba.ar The Third Moscow Solar System Symposium 3M-S3 Space Research Institute, Moscow, Russia, October 8-12, 2012

2. Introduction B • 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. After Saunders and Russell, 1986 V  Ec = - V x B Mars Dubinin et al., 2006

3. Outline • Tail morphology • Magnetic field topology (magnetotail). • Plasma regions. • Energetics and dynamics • Conclusions • Outstanding questions

4. Magnetic morphology

5. 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. Saunders and Russell, 1986 Venus magnetotail N = 70 IMB = 50% N= 48 B +B’x -B’x -10RV > XVSO >-12RV B Ec VEX MAG Zhang et al., 2010

6. Mars’ magnetotail B 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). Yeroshenko et al., 1990 Zhang et al., 1994 Average 13o

7. Titan’s magnetotail: variability sources Apart from the MP proximity and SLT effect... Titan’s distance to Saturn disk changes seasonally... Kronian field stretch @ Titan orbit Southern summer Bertucci, et al., 2009 So, every ~10.8 hours all this happens.... 1 2 and during a planetary period ... 10.8 h Titan’s orbit 3 4 after Khurana et al., 2009 Bertucci, 2009

8. Titan’s magnetotail: magnetic structure Tail lobe fields and polarity reversal are compatible with upstream V-B geometry (e.g. Neubauer et al., 1984, 2006, Bertucci et al., 2007). North Lobe Backes et al., 2005 TA flyby (1.4 RT distance) South Lobe T9 flyby (~5 RT distance) V Departure from nominal flow as much as 40° (Bertucci et al., 2007, Szego et al., 2007, McAndrews et al., 2009). Tail

9. Plasma morphology

10. Plasma morphology - Venus Phillips and McComas (1986) • 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). Pre-VEX VEX (Solar Min) H+ flux E> 300 eV m/q=14 flux E> 300 eV Fedorov et al., (2008), see also Fedorov et al., 2011

11. Plasma morphology - Mars M/q =1-2 flux E/q> 300 eV M/q>14 flux E/q > 300 eV • 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 Ec Fedorov et al., 2006 Heavies M/Q >14

12. 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). Plasma morphology - Titan T9 flyby Flow Tail 1 2 Bertucci,et al.,, Coates, et al., 2007 n > 5 cm-3 Flow Ec Modolo et al., 2012, in preparation

13. Energetics and dynamics

14. Z Venus  O x O  x Y • 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) Fedorov et al., 2008

15. Mars Dubinin et al., 1993 • 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) Plasma sheet Ion extraction by Ec penetration in BL Dubinin et al (2006)

16. Titan Tail • 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. Electrons Ions B polarity reversal layer DAYSIDE

17. 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.