1. In-situ observations of magnetic reconnection in solar system plasma What can we export to other astrophysical environments? Alessandro Retinò, R. Nakamura and W. Baumjohann Space Research Institute, Austrian Academy of Sciences, Graz, Austria A. Vaivads Swedish Institute of Space Physics, Uppsala, Sweden D. Sundkvist and F. S. Mozer Space Sciences Laboratory, University of California, Berkeley, USA F. Sahraoui Laboratory of Physics of Plasmas, CNRS, Paris, France MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

2.  Motivation  Magnetic reconnection: basics, importance, universality  Collisionless reconnection in near-Earth space  In-situ observations of turbulent reconnection: first evidence energy dissipation particle acceleration  Possible comparisons with other astrophysical environments: heating of the solar corona cosmic ray acceleration  Summary Outline 2 MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

3. Motivation 3 MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at Magnetic forms produce activity and violence in the otherwise serene thermal degradation of the cosmic landscape [E.N. Parker]  Magnetized plasma ubiquitous in the universe  Key processes in magnetized plasma: dynamo, reconnection, MHD instabilities,...  In-situ observations required to understand the basic physics  Synergy between in-situ & remote observations important [ESA/SOHO-EIT in EUV][NASA/HBT in UV] [NASA/HBT-FCO in UV]

4. Violation of the frozen-in condition 4 Frozen-in E' =E+VxB=0 E || =0 [ Paschmann, Nature, 2006] Reconnection: basics No frozen-in E' =E+VxB=J/  E || ≠0 (  conductivity in the diffusion region) MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

5. 5 [Vaivads et al., Space Sci. Rev., 2006] Breaking of frozen-in condition -> ->local topology change -> ->large-scale:  reconfiguration of magnetic fields  energy conversion/dissipation: plasma acceleration (Alfvénic) plasma heating particle acceleration  plasma transport Reconnection: importance E' E' is the reconnection rate MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

6. Laboratory plasma [Intrator et al., Nature Physics, 2009] near - Earth space [Paschmann et. Al, Nature, 1979] [Hones et al., Geophy. Res. Lett., 1984] [Phan et al., Nature, 2006] [Retinò et. al, Nature Physics, 2007] also observed at Mercury, Mars & Saturn Solar corona [Yokoyama et. al., ApJ Lett., 2001] 6 Reconnection: universality mfp ~ 1 A. U. collisionless plasma

7. In-situ vs remote observations 7 MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at LABNEAR-EARTHSUNASTRO Direct measur. of E & B yesyes (high res)nono Direct measur. of f(v)noyes (high res)nono Imagingnonoyes (high res)yes Boundary conditionscontrollednaturalnaturalnatural Repeatabilityyesnonono Number of objectsa fewoneonemany  direct mesurements of E, B and f(v) required to resolve the basic physics of reconnection!  near-Earth space best laboratory (so far)  comparison with remote observations important

8. Near-Earth observations: Cluster spacecraft 8 MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at  ESA cornerstone mission  first 4 spacecraft mission !  distinguish temporal/spatial variations  measurement of 3D quantities: J=(1/μ 0 )  xB,  B = 0, E  J,...  tetrahedrical configuration with changeable spacecraft separation 100-10000 km -> measurements at different scales 4 sets of 11 identical instruments to measure:  magnetic field  electric field  thermal particle distribution functions  suprathermal particle distribution functions FGM magnetometer http://sci.esa.int/science-e/www/area/index.cfm?fareaid=8

9. Collisionless reconnection MHD anomalous conductivity ? Hall electron pressure ? electron inertia ? Three scales: MHD ( >>  i ) 10 3 – 10 4 km ion ( ~  i ) 50-500 km electron ( ~  e ) 1-10 km [NASA/MMS] large-scale laminar current sheet (e.g. magnetotail)

10. Reconnection rate Reconnection first proposed by Giovanelli [Nature, 1946] to explain solar flares Sweet-Parker reconnection: rate ~ (R m ) -1/2 ~ (  ) -1/2 depends on resistivity -> SLOW (flare ~100s) Collisionless reconnection: rate ~ 0.1independent on resistivity -> FAST !!! Numerical simulations [Birn, JGR, 2001] Spacecraft data [Mozer et. al., Phys. Rev. Lett., 2002] [Vaivads et al., Phys. Rev. Lett., 2004] [Retinò et al., Nature Physics, 2007]

11. Turbulent reconnection: important for astrophysical plasma?  Turbulence and reconnection ubiquitous in the universe: turbulent reconnection should be common in astrophysical plasmas  Turbulent configuration could increase the reconnection rate wrt laminar case: faster reconnection  Turbulent reconnection could be important for energy dissipation  Larger electric fields and small-scale irregularities could enhance particle acceleration MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

12. Turbulent reconnection [Matthaeus, Phy. Fluids, 1986] B Small-scale laminar current sheet in turbulent plasma Turbulent current sheet [adopted from Lazarian & Vishniac,1999] Turbulence in laminar current sheets [Bale et al. 2002, Vaivads et al., 2004, Retinò et al., 2006] Which configuration ? MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

13. In-situ evidence of turbulent reconnection 13 cartoon of current sheet formation in turbulent plasma (contours are magnetic field lines) [Retinò et al., Nature Physics,2007] also in solar wind [Gosling et al., ApJ,, 2007] volume-filling current sheets reconnecting current sheets energetic ions First evidence !

14. Small-scale laminar current sheet in turbulent plasma 14 single spacecraft four spacecraft (assumptions: planarity & stationarity) SC separation ~ 100 km turbulence ? turbulent current sheet ? R ~ 0.1 (fast rec) MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

15. Energy dissipation 15 Alfvenic turbulence (E/B ~Va) E&B Kolmogorov-like [ Sundkvist et al., PRL,2007] Turbulence properties Intermittency Gaussian ii i measured dissipation rate comparable with that expected from waves around ion gyrofrequency: turbulent reconnection in volume-filling current sheets can be important energy dissipation mechanism ! [ Servidio et al., Phy. Plasma, 2010] Large number of reconnection regions

16. Particle acceleration 16 suprathermal ions B First order Fermi acceleration during fast reconnection in turbulent current sheet [Lazarian et al., 2010] Particle acceleration in small-scale current sheet in turbulent plasma [Dmitruk & Matthaeus, JGR, 2006] No clear evidence (so far) of particle acceleration from in-situ data !

17. Comparison with other astrophysical plasma 17 [Vaivads et al., Plasma Phys. Contr. Fus., 2009] Can we directly export results from in-situ observations to other astrophysical environments? Caution is needed: (most)solar system plasma are:  fully ionized  mainly H +, e -  not relativistic (Va<<c)  collisionless MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

18. Possible comparisons (TBD) 18 The magnetic carpet on the Sun [From SOHO/SOI http://soi.stanford.edu] Heating of the solar chromosphere/corona: small-scale reconnection events [Shibata et. al, Science, 2007] Cosmic ray acceleration:  Giant radio galaxies [Kronberg et al., Ap. J. Lett., 2004]  Anomalous cosmic rays (5-100 MeV/nucleon) [Lazarian et. al, ApJ, 2009; Drake et al., ApJ, 2010] MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at

19.  Reconnection universal energy conversion/dissipation process  In-situ observations required to resolve the basic physics  Fast collisionless reconnection is observed in-situ in the solar system e.g. in near-Earth space  First experimental evidence of turbulent reconnection obtained in near-Earth space. Turbulent reconnection important for energy dissipation and (possibly) for particle acceleration.  Results from in-situ observations may be exported to distant astrophysical environments but much caution is needed. Crucial first to understand differencies and similarities between environments.  Possible examples for turbulent reconnection: heating of solar corona and cosmic ray acceleration 19 Summary MFPO conference - Krakow 2010 alessandro.retino@oeaw.ac.at