Dynamics of solar wind protons reflected by the Moon

Mats Holmström, M. Wieser, S. Barabash, Y. Futaana Swedish Institute of Space Physics Kiruna, Sweden

A. Bhardwaj Space Physics Laboratory, Vikram Sarabhai Space Center, Trivandrum, India

Fall AGU, 2009 Wed December 16, 10:50 to 11:05 AM P32A­03 307 (Moscone South) [email protected] www.irf.se/~matsh/ Overview

● Observations of proton fluxes near the Moon by – Apollo SIDE – Nozomi – Kaguya (Selene) – Chandrayaan­1 ● Modeling of reflected solar wind protons Apollo SIDE observations

Energetic Ion Bursts on the Nightside of the Moon, J.W. Freeman, Jr., JGR, v. 77, n. 1, 1972 Nozomi observations

1

2 2 1

1 2

Moon-related nonthermal ions observed by Nozomi: Species, sources, and generation mechanisms, Futaana, et al., JGR, 108(A1), 1025, 2003 Reflected solar wind protons

Kaguya. Nishino et al., GRL 2009 Chandrayaan­1 observations

Approx. ecliptic plane (a) (b) Gyro motion of reflected protons

2v v =0 0 0 B solar SW v 3v wind

-v v =-v 0

E SW

u SW B SW Proton fluxes in the wake

Wake entry possible for reflected E SW protons

Depending on IMF

(Nishino et al., GRL 2009, u SW Type-II entry) B SW Reflection models

θ θ θ θ

specular perpendicular cos2perpendicular cos2specular Test particle model of reflected protons

B u SW SW

z y z E y SW x x Hybrid model results

B u SW SW

1 1 2 2

1 z y z E y SW 2 x x

Similar results (away from wake) as a test particle model (constant IMF) => test particles can be used Comparison with Nozomi observations

1 1000 1000 [km/s] [km/s] z z v v

-1000 -1000 -1000 v [km/s] 1000 -1000 v [km/s] 1000 perp para 1000 1000 2 [km/s] [km/s] z z v v

B SW B -1000 -1000 SW -1000 v [km/s] 1000 -1000 v [km/s] 1000 perp para

Test particle model Observations

Model IMF similar to IMF during Nozomi observations Gray = solar wind protons, Black = reflected protons cos2specular reflections gave best fit (shown above) Velocity spectrum of (all) reflected protons

Solar wind

100 200 300 400 500 600 700 [km/s] Changing solar wind conditions

1000 1000 [km/s] [km/s] z z v v

-1000 -1000 1000 1000 [km/s] [km/s] z z v v B B SW B SW B SW SW -1000 -1000 -1000 v [km/s] 1000 v [km/s] 1000 -1000 v [km/s] 1000 v [km/s] 1000 perp para perp para Summary

● Solar wind protons reflected by the Moon can explain – Nozomi observations – Kaguya observations – Chandrayaan­1 observations – Apollo SIDE observations (maybe)

● A local process that affects the global solar wind interaction

● A universal process that occur at all bodies without a significant atmosphere. See the poster P43B­1431, Strong interaction between Phobos and the solar wind, Futaana et al., Thursday, December 17, 1:40 PM

● This study will appear in JGR