Distant magnetotail dynamics of Earth-like planetary magnetospheres

1. Distant magnetotail dynamics of Earth-like planetary magnetospheres Z.Vörös (1), M.L. Khodachenko (1), G. Facskó (2),A. Runov (3), P. Janhunen (2), and M. Palmroth (2) Space Research Institute, Austrian Acad. Sci., Graz, Austria (zoltan.voeroes@oeaw.ac.at) (2) Finnish Meteorological Inst., Helsinki, Finland (3) Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, USA. European Planetary Science Congress 2012, IFEMA-Feria de Madrid 23 – 28 September 2012, Madrid, Spain Sibeck et al., 2011

2. Outline • Energetic neutral atom (ENA) observations of the Earth‘s magnetotail and the Moon • Reconnection statistics in the distant magnetotail • Magnetotail response to the directional changes and pressure pulses in the solar wind • Lessons for the Earth-like magnetospheres

3. ENA fluxes and observations ENAs are energetic ions neutralized through charge exchange collisions with cold neutrals. Therefore, the ENA and ion fluxes are related by (e.g. Fuselier et al., 2010): where - energy and position dependent ENA flux - energy and position dependent ion flux • energy dependent charge exchange cross-section - neutral atom (hydrogen) density at

4. ENA fluxes and observations Credit: NASA/Goddard Space Flight Center  • Sources of energetic ions: • the solar wind • accelerated ions in the • magnetosphere • Sources of cold neutrals: • the geocorona • the Moon Our interest: the magnetotail

5. ENA observations of the Earth‘s magnetotail Elliptical polar orbit IMAGE ENA measurements converted to ion temperatures in the magnetotail IMAGE jet of tailward moving hot plasma: plasmoid Keesee et al., 2008

6. IBEX ENA tail observations 0.5 – 6 keV energy range McComas et al. 2011 IMAGE: oblique viewing of the plasma sheet from inside of the magnetosphere IBEX: views the magnetotail from the side and from outside of the magnetosphere Disconnection event , plasmoid??

7. Observation of ENAs during a geomagnetically quiet time! The dynamic pressure of the solar wind increased by a factor of 2. • Possible interpretations: • Enhancement of SW pressure can • lead to tail compression, adiabatic • heating and energetic ions. • However, the geocorona is • very tenuous in the tail. •  Energetic ions can be accelerated • by reconnection in the tail.

8. First observations of ENAs from the Moon by IBEX McComas et al. 2009 nonlinear! Backscattered ENAs from the Moon were not observed before IBEX! Lunar ENA albedo is ~ 10% Moon associated hydrogen can increase the density of neutrals in the tail! Two probes of the ARTEMIS mission are co-moving with the Moon, crossing the magnetotail once per month. It is reasonable to investigate the dynamics and motion of the magnetotail at the distance of the Moon using ARTEMIS data. We are interested in processes which can accelerate ions at the distance of the Moon in the tail.

9. Reconnection statistics at the distance of the Moon

10. Fast plasma flows in the plasma sheet (beta>1) are associated with magnetic reconnection. Magnetic reconnection is in progress at or near the probes when the ratio of the flux of 5-keV to that of 1-keV electrons is higher than 1.5. These are highly accelerated electron events (HAES) (Nagai et al. 2005). (Vörös, 2011) Magn. recon. HAES ARTEMIS electron-flux-ratio distribution (Vörös et al., 2012) Oct. 2010 – June 2011

11. ARTEMIS measurements of reconnection associated HAES and fast flows in the plasma sheet between Oct. 2010 and June 2011 (Vörös et al., 2012). During 9 double tail crossings there were 14 HAES. Some of these events (e.g. in February 2011) were observed by both THB and THC. Between 1995 and 2003, during winter and spring seasons, GEOTAIL observed 34 HAES in the mid-tail (Nagai et al., 2001) It suggests that the tail region at the distance of the Moon is rather active and can play an important role in global magnetosphericphysics.

12. Pressure pulses in the solar wind & large-scale motions of the magnetotail

13. Large scale motionand compression of the tail P1 (THB) P2 (THC) V~ - 400 km/s <V> ~ 0 km/s TAIL • is the angle between radial direction (Sun-Earth) and SW speed • vector

14. GUMICS-4 global MHD simulations of the large-scale motions of the tail: The plasma sheet is shrinked and shifted mainly in the X-Y plane during the tailward flow intervals. GUMICS-4 code: Janhunen et al., 2012 -60RE X-Y plane THB THC ION DENSITY 7o The magnetotail reacts to the solar wind flow directional changes over a time scale of tens of minutes (Sergeev et al. 2008).

15. P2 (THC) Large-scale movement of the tail Field, plasma and particle data Strahl (contrapropagating) electrons on magnetotail field lines indicate a connection of magnetotail field lines to the IMF (open field line geometry). Strahl electrons in the SW indicate closed IMF lines with foot-points on the Sun. P1 (THB)

16. Riley et al., 2006 How often plasma flow directional changes occur in the solar wind? Yurchyshyn et al., 2005

17. Sunspot #

18. Directional changes of the plasma flow in the solar wind Over threshold Below Thresh. • Plasma flow directional changes of • few degrees with leghts of tens of • minutes occur 10-20 times per day. • Longer intervals are associated with • larger deviations. • The associated compressions • and motions of the magnetotail, • including possible adiabatic • acceleration of ions can be rather • frequent at the distance of the • Moon. • high probability for producing • ENAs in the distant tail.

19. Solar cycle dependence of directional changes.

20. CONCLUSIONS • The magnetotail beyond X = - 30 RE is rather active, • in comparison with mid-tail data, the number of • reconnection associated HAEs and fast flows is high; • The large-scale motion and shrinking of the plasma • sheet at X ~ -60 RE is associated with directional changes • of the solar wind and increased static and kinetic pressures. • The large-scale motions and tail compressions can • trigger reconnection or/and heat adiabatically the tail • high fluxes of energetic ions in the tail combined • with neutrals from the Moon can produce ENAs.

21. Where are the neutrals near observable exoplanets? • 2 scenarios: • ENA clouds can expand beyond the • protecting magnetopauses near M-type • host stars (Lammer et al.) Stellar wind- • hydrogen-cloud interactions are important • - enhanced ENA emissions are produced • due to the activity in the tail. The distant • tail is more active as it was previously • believed. Earthward flows can interact with • the denser hydrogen corona near a planet; • or tail activity can drive the interaction of • ions with a Moon associated neutrals.