1. 1 Two mechanisms of solar-wind proton entry deep into the near-Moon wake revealed by SELENE (KAGUYA) STP seminar August 26, 2009 Masaki N. Nishino* 1 Collaborators: Masaki Fujimoto 1, Kiyoshi Maezawa 1, Yoshifumi Saito 1, Shoichiro Yokota 1, Kazushi Asamura 1, Takaaki Tanaka 1, Hideo Tsunakawa 2, Hidetoshi Shibuya 3, Masaki Matsushima 2, Hisayoshi Shimizu 4, Futoshi Takahashi 2, and Toshio Terasawa 2 (1)ISAS/JAXA, (2) TITECH, (3) Kumamoto Univ., (4) ERI, Univ of Tokyo

2. 2 Outline Introduction SELENE spacecraft & instruments Proton reflection at the dayside surface (Saito et al. GRL, 2008) Type-1 entry (Nishino et al. GRL, 2009) Type-2 entry (Nishino et al. GRL, in press) Summary

3. 3 More than 80 % of time... The moon stays in the solar wind –interaction btwn SW and the Moon Why important ? –Wake formation behind the moon –Particle/dust acceleration –Hazardous in future missions –Space plasma and planetary surface no thick atmosphere no intrinsic magnetic field

4. 4 A traditional view of the lunar wake Electron-rich –high thermal speed of e- –generation of E field Gradual acceleration of SW ions No solar wind ions How do ions behave in the near-Moon wake ? E E

5. 5 Wind and SELENE Comparison of wake observations by Wind and SELENE WindSELENE (KAGUYA) detectorions + electrons altitude11,000 km100 km SW proton intrusion gradual intrusion in the distant wake along IMF ? interpretationfluid-type ?

6. 6 Outline Introduction SELENE spacecraft & instruments Proton reflection at the dayside surface Type-1 entry Type-2 entry Summary

7. 7 SELENE (Kaguya) spacecraft Launch –on Sept. 14, 2007 Orbit –polar orbit –2-hour period –3-axis stabilized Plasma measurement –Ions (composition) –Electrons –Magnetic fields –Waves

8. 8 MAP (PACE+LMAG) onboard SELENE (Kaguya) Orbit 2-h period polar orbit 100 km alt. MAP-PACE electrons x2 ions x2 each 2  str. FOV MAP-LMAG magnetic field 32 Hz MAP measures the near-Moon plasma environment comprehensively.

9. 9 Outline Introduction SELENE spacecraft & instruments Proton reflection at the dayside surface Type-1 entry Type-2 entry Summary

10. 10 Solar-wind proton reflection at the dayside surface protons reflected/scattered at the dayside surface

11. 11 Outline Introduction SELENE spacecraft & instruments Proton reflection at the dayside surface Type-1 entry –Observation –Model calculations Type-2 entry Summary

12. 12 Ion energy gain & loss at wake boundary (1) SP: acceleration NP: deceleration down e- up e- down ion up ion up ion daySPwakeNP daySPwakeNP gainlossgainloss

13. 13 Ion energy gain & loss at wake boundary (1) SP: acceleration NP: deceleration gainlossgainloss

14. 14 Ion energy gain & loss at wake boundary (1) SP: acceleration NP: deceleration gainlossgainloss

15. 15 Ion energy gain & loss at wake boundary (1) SP: acceleration NP: deceleration gainlossgainloss

16. 16 Ion energy gain & loss at wake boundary (1) SP: acceleration NP: deceleration gainlossgainloss

17. 17 Ion energy gain & loss at wake boundary (1) SP: acceleration NP: deceleration gainlossgainloss

18. 18 Dependence on SW magnetic field By By>0 Implication of particle dynamics By<0 small By SP: gain NP: loss SP: loss NP: gain no energy gain nor loss

19. 19 Outline Introduction SELENE spacecraft & instruments Type-1 entry –Observation –Model calculations Type-2 entry Summary

20. 20 Larmor phase filtering effect ? Wake E field ? E E Vx decreases Vx increases

21. 21 Wake E-field model How does this simple E field change the SW proton energy ?

22. 22 Model calculations : SW proton intrusion (a) No E field no acceleration cutoff due to thermal motion (b) with E field energy gain & loss no energy change energy gainenergy loss observed ions SW By=4 nT Vsw=350 km/s Vth=35 km/s wake potential 300 eV, (width Rm/4, E ~ 0.7 mV/m)

23. 23 Model calculations : SW proton intrusion Trajectory of SW protons intrusion to mid- and low- latitude region Energy in the rest frame gain and loss Energy in the SW frame gain (as much as wake potential) bulk: Vsw=350 km/s, Larmor: v=70 km/s

24. 24 Summary of Type-1 entry Solar wind protons can easily access to the lunar night side. Before SELENE Now with SELENE Complicated plasma environment We are now constructing a new model.

25. 25 Outline Introduction SELENE spacecraft & instruments Proton reflection at the dayside surface Type-1 entry Type-2 entry –Observation –Model calculation Summary

26. 26 Ion found in the deepest wake 2 kinds of wake ? (1)almost vacuum (2)plasma entry

27. 27 Proton entry into the deepest wake Proton sneaking into the deepest wake (from dayside ?) Accompanied by bi-streaming e- By-dominant IMF SZA 168 deg 100 km height

28. 28 Obliquely-going protons are detected by IMA Protons turn upward just near the nightside surface E-t scatter plot along virtual spacecraft orbit g E-t scatter plot along the virtual spacecraft orbit scatter location : every 5 degrees in the dayside region of Lon. and Lat. -70~+70 deg) scatter angle : every 2 degrees

29. 29 Validity of our model of Type-II entry Similar patterns related to Type-II entry are reproduced.

30. 30 Formation of PGR (proton-governed region) Scattered protons sneak into one hemisphere on the nightside formation of PGR Generation of outward E field around PGR PGR absorbs ambient electrons along the IMF counter-streaming electrons are found in the PGR

31. 31 Wind and SELENE Comparison of wake observations by Wind and SELENE WindSELENE (KAGUYA) detectorions + electrons altitude11,000 km100 km SW proton intrusion gradual intrusion in the distant wake along IMF Two types in the near-Moon wake perp. to IMF interpretation fluid-type electron dominant particle dynamics formation of PGR

32. References Ogilvie et al. GRL 1996 Halekas et al. JGR 2005 Saito et al. GRL 2008 Nishino et al. GRL 2009a Nishino et al. GRL 2009b 32