STP seminar August 26, 2009 Masaki N. Nishino * 1

1. Two mechanisms of solar-wind proton entrydeep into the near-Moon wake revealed by SELENE (KAGUYA) STP seminar August 26, 2009 Masaki N. Nishino*1 Collaborators: Masaki Fujimoto1, Kiyoshi Maezawa1, Yoshifumi Saito1, Shoichiro Yokota1, Kazushi Asamura1, Takaaki Tanaka1, Hideo Tsunakawa2, Hidetoshi Shibuya3, Masaki Matsushima2, Hisayoshi Shimizu4, Futoshi Takahashi2, and Toshio Terasawa2 ISAS/JAXA, (2) TITECH, (3) Kumamoto Univ., (4) ERI, Univ of Tokyo

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. 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. 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 E E How do ions behave in the near-Moon wake ?

5. Wind and SELENE Comparison of wake observations by Wind and SELENE

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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. Wind and SELENE Comparison of wake observations by Wind and SELENE

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