Martian Pick-up Ions (and foreshock): Solar-Cycle and Seasonal Variation M. Yamauchi(1); T. Hara(2); R. Lundin(3); E. Dubinin(4); A. Fedorov(5); R.A. Frahm(6); Y. Futaana(1); R. Ramstad(1); H. Nilsson(1); M. Holmstrom(1); S. Barabash(1) (1) Swedish Institute of Space Physics (IRF), Kiruna, Sweden; (2) Space Sciences Laboratory, University of California, Berkeley, USA; (3) IRF, Umea, Sweden; (4) Max-Planck-Institut fur Sonnensystemforschung, Germany; (5) Institut de Recherche en Astrophysique et Planetologie (IRAP), CNRS/Universite de Toulouse, France; (6) Southwest Research Institute, USA

R S : Bow-shock radius ( ~ 5000 km for Martian Subsolar) M A : Alfvén Mach number r g : Gyroradius ( ~ 1000 km for 2 keV H + under 6 nT) c/  pi : Inertia length ( 100 km for 5/cm 3 H + ) RSRS MAMA c/  pi R S r g /R S cold H+ at BSforeshock Earth 5~ 1.2~ 0.3~ 0.4noyes Venus very littleyes Mars~ 0.5~ 1.4~ 5~ 8someless Comet? 1~2large massive? Venus-Mars-Comet difference Planetary Size & Gravity  Standoff distance & Exospheric Size  Cold ion inside Solar Wind / Bow Shock

Actual observation (scan over  ) pickup ions BS SW foreshock No clear pickup ion SW reflection occurs but no foreshock at X>0 SW reflection

Cold ion density outside Bow Shock varies with exospheric extent (visible~UV) and ion production rate (UV). Next: Solar Cycle dependence Season: Sun-Mars distance changes 20% (radiation flux 45%)

Observation Probability note: automated method is far from perfect (e.g., including reflected ions near bow shock), but statistics is clear (using automated method to identify ring) – – – – –4 Southern Summer (tilt angle) ≈ short distance – – – –6 Southern Winter (tilt angle) = long distance 100% 50% 0%

No Hemispheric difference North Summer (distant)South Summer (close) S hemisphere N hemisphere S hemisphere N hemisphere 100% 50% 0%

It looks like 1. Season >> Solar cycle (clear) 2. Not only UV level (need to confirm)  Statistic by Manual Method (examine data by eye) Summer during Solar Minimum (bow shock is longer distance!) produces more pick-up ions than Winter during Solar Maximum

Reflected ions also forms "ring"  "probability" is high near bow shock

Manual (eye) examination statistics 2-month averaged result

Compared with UV level Summer during Solar Minimum (bow shock is longer distance!) >> Winter during Solar Maximum Probability of clear pick-up ions

(1) Intensity of the ring ions varies by at least one order of magnitude by variable Sun-Mars distance. (2) For the same UV flux level, Summer during Solar Minimum produces more pick-up ions in the solar wind than Winter during Solar Maximum  not only UV (3) Ring ions is strong close to bow shock (inside regions full of reflected ions)  not only UV (4a) Ring ions sometime appear less than one day during Winter, and (4b) disappear for some period during Summer (difficult to attribute this to IMF variability).  not only UV Summary

Implication Electron impact ionization? Exosphere breeds? Alfven's critical ionization process? (foreshock creates ring?) Production of pick-up ions is very variable in the independent way from solar radiation.

Related to pick-up ions (1) Fate of pick-up ions: Comet-like diffusion (2) O + sneaking out event to upstream (3) Relation to Foreshock

(1) Diffusion of pick-up ions Similar to comet! X≈+1 R M X≈  1.5 R M

(2) Oxygen outside bow shock No O+ pick-up from O-corona, but can be picked up

(3) Foreshock 2005: almost none 2007: sometimes 2008: sometimes 2009: rare 2010: sometimes 2011: rare

Foreshock vs pick-up ions Except 2007 June-September (Martian summer), foreshock during Martian summer (out of phase from pick-up ion. Solar cycle (UV) might play some role in this cases foreshocks

Note Although anti-phase, we do observe co-existence of Foreshock with pick-up ions (rare event)

Conclusion Martian upstream is a real plasma laboratory that the Earth cannot provide. Just related to the pick- up phenomenon, many unknown physics exist. Martian pick-up ion physics is a good reference for Comet pick-up ion physics

Thank you

we need to classify all “non-solar wind” ions because the Martian upstream is full of reflected ions, pickup ions, and thermalized form of these ions. For sold probability work, In 2011 paper, we reported that we could not find foreshock in 2005 data (we used highest post-acc data). (comet-like) scattered pick-up ions Foreshock Reflected (and accelerated) at bow shock Detached Bow shock

ring distribution in SW 2005: rare & – / often & : rare – / some – 12 often : rare – : rare – 3 & – 12 / some – 10 often : rare –10 / some – : rare –12 / some – 2 often : rare –7 & –10 / some & – rare / some often –

pick-up ions (ring distribution) bow shock

upstream pick-up

downstream pickup = comet-like scatter

comet-like scatter

pick-up + reflected

Reflected with pick-up ions

Reflected without pick-up ions

Reflected ⇒ Foreshock

foreshock boundary

detached bow shock

(1) Gravity: Venus > Mars < comet  (2) Exosphere: Venus < Mars < comet  (3) newly born H+ in Solar Wind: Venus < Mars < comet  (4) Bow shock: Venus ≠ Mars ≠ comet Venus-Mars-Comet difference: cold H +