Transcript Martian Pick

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
Venus-Mars-Comet difference
Planetary Size & Gravity  Standoff distance & Exospheric Size
 Cold ion inside Solar Wind / Bow Shock
RS
Earth
5
Venus
1
Mars
~ 0.5
Comet ?
MA
c/piRS rg/RS
cold H+ at BS foreshock
~ 1.2 ~ 0.3
~ 0.4 no
yes
1
1
~ 1.4 ~ 5
1~2 large
1
very little
~8
some
large massive
yes
less
?
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+)
Actual observation (scan over )
pickup ions
SW reflection
foreshock
SW
SW
BS
No clear pickup ion
BS
SW reflection occurs
but no foreshock at X>0
Next: Solar Cycle dependence
Cold ion density outside Bow Shock varies with exospheric
extent (visible~UV) and ion production rate (UV).
Season: Sun-Mars distance changes 20% (radiation flux 45%)
Observation Probability
(using automated method to identify ring)
note: automated method is far from perfect (e.g., including
reflected ions near bow shock), but statistics is clear
Southern Summer (tilt angle) ≈ short distance
2005.6–8
2007.7–9
2009.3–7
2011.3–6
Southern Winter (tilt angle) = long distance
2013.1–4
100%
50%
2004.6–10
2008.4–9
2010.3–8
2012.2–6
0%
No Hemispheric difference
South Summer (close)
North Summer (distant)
S hemisphere
S hemisphere
100%
50%
0%
N hemisphere
N hemisphere
It looks like
1. Season >> Solar cycle (clear)
2. Not only UV level (need to confirm)
Summer during Solar Minimum (bow shock is
longer distance!) produces more pick-up ions than
Winter during Solar Maximum
 Statistic by Manual Method
(examine 2005-2012 data by eye)
Reflected ions also forms "ring"
 "probability" is high near bow shock
Manual (eye) examination statistics
2-month averaged result
Compared with UV level
Probability of clear pick-up ions
Summer during Solar Minimum
(bow shock is longer distance!)
>> Winter during Solar Maximum
Summary
(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
Implication
Production of pick-up ions is very variable in the
independent way from solar radiation.
• Electron impact ionization?
• Exosphere breeds?
• Alfven's critical ionization process?
(foreshock creates ring?)
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
X≈+1 RM
X≈-1.5 RM
Similar to
comet!
(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
foreshocks foreshocks
foreshocks
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
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 pickup phenomenon, many unknown physics exist.
Martian pick-up ion physics is a good reference
for Comet pick-up ion physics
Thank you
For sold probability work,
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.
(comet-like) scattered
pick-up ions
Foreshock
Reflected (and
accelerated) at bow shock
Detached Bow shock
In 2011 paper, we reported that we could not find foreshock in
2005 data (we used highest post-acc data).
ring distribution in SW
2005: 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
bow shock
pick-up ions (ring distribution)
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
Venus-Mars-Comet difference:
cold H+
(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