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);

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

RS: Bow-shock radius (~ 5000 km for Martian Subsolar)

MA: Alfvén Mach number

rg: Gyroradius ( ~ 1000 km for 2 keV H+ under 6 nT)

c/pi: Inertia length (100 km for 5/cm3 H+)

RS MA c/piRS rg/RS cold H+ at BS foreshock

Earth 5 ~ 1.2 ~ 0.3 ~ 0.4 no yes

Venus 1 1 1 1 very little yes

Mars ~ 0.5 ~ 1.4 ~ 5 ~ 8 some less

Comet ? 1~2 large large massive ?

Venus-Mars-Comet differencePlanetary Size & Gravity Standoff distance & Exospheric Size

Cold ion inside Solar Wind / Bow Shock

Actual observation (scan over )

pickup ions

BS BS

SW SW

foreshock

No clear pickup ionSW 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)

2005.6–8 2007.7–9 2009.3–7 2011.3–6 2013.1–4

Southern Summer (tilt angle) ≈ short distance

2004.6–10 2008.4–9 2010.3–8 2012.2–6

Southern Winter (tilt angle) = long distance 100%

50%

0%

No Hemispheric differenceNorth 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 2005-2012 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 RM

X≈1.5 RM

(2) Oxygen outside bow shock

No O+ pick-up from O-corona, but can be picked up

(3) Foreshock

2005: almost none

2007: sometimes2008: sometimes

2009: rare2010: sometimes2011: 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 foreshocksforeshocks

NoteAlthough 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 SW2005: rare 2005.1 - 2005.5 & 2005.9 – 2005.10 / often 2005.7 & 2005.11

2007: rare 2007.1 – 2007.4 / some 2007.9 – 12 often 2007.6 - 2007.8

2008: rare 2008.1 –12

2009: rare 2009.1 – 3 & 2009.11 – 12 / some 2009.4 – 10 often 2009.8

2010: rare 2010.1 –10 / some 2010.11 – 12

2011: rare 2011.8 –12 / some 2011.1 – 2 often 2011.3 - 2011.6

2012: rare 2012.1 –7 & 2012.9 –10 / some 2012.8 & 2012.11 –12

2013 rare 2012.8 / some 2012.9 often 2012.2 – 2012.3

pick-up ions (ring distribution)

bow

sho

ck

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+