MarcoPolo-R Cosmechemistry Workshop @CNES, Paris, December 18, 2012
Outline of Hayabusa sample initial analysis
and recent progress on “space weathering”. A. Tsuchiyama
Division of Earth and Planetary Sciences
Graduate School of Science
Kyoto University
Hayabusa mission
©小
小野瀬直美・奥平恭子
May 9, 2003
Launch
Sep.-Nov. 2005
Arrival to Itokawa
Remote Sensing
Sampling
Jun 13, 2010
Return to Earth
Curation started
Jan.-Dec. 2011
Initial analysis
Jun. 2012
AO analysis started
Hayabusa sample initial analysis: Outline (1)  Material on Itokawa surface: Origin of meteorites
ü  LL chondrites: (EPMA, µCT, NAA, SIMS) [1-4,7]
ü  Rubble pile asteroid: (EPMA, µCT) [1,2]
(2) Regolith particles: Processes on Itokawa’s surface
µCT) [2]
ü  Impact fragments (3D shapes) (µ
ü  Space weathering rim (Fe nanoblobs) (STEM/TEM) [5]
ü  Solar wind (SW) implantation (Noble gas) [6]
ü  Grain abrasion (surface morphology) (µ
µCT) [2]
ü  Impact features (FE-SEM) [7]
[1] Nakamura T. et al. (2011) Science
[2] Tsuchiyama A. et al. (2011) Science
[3] Ebihara M. et al. (2011) Science
[4] Yurimoto H. et al. (2011) Science
[5] Noguchi T. et al. (2011) Science
[6] Nagao K. et al. (2011) Science
[7] Nakamura E. et al (2012) PNAS
SR-based Microtomography at SPring-8
Microtomography plays an important role in the initial analysis.
ü  3D mineralogy and petrography ⇒ Itokawa material
ü  3D shapes ⇒ Itokawa regolith
ü  Design for later destructive analyses
50 µm
Projection inages
CT images (8 keV)
Sample: RA-QD02-0031
3D shape
Tsuchiyama+ （2011)
Surface processes: Recent progress
ü  Evolution of space weathering rim [1,2]
Blisters by SW He implantation
Time scale (~103 yr.)
ü  Solar flare tracks [1]
ü  Grain abrasion in nano-scale [2]
blisters [1]
[1] Noguchi+ (2012) TEM/STEM
[2] Matsumoto+ (2012) FE-SEM
Escape from surface
Micrometeoroids
Space weathering
rim formation
Grain abrasion
Galactic
Solar wind
cosmi
c ray
solar flare tracks [1]
Itokawa (rubble
pile asteroid)
Grain motion
⇒ Comprehensive understandings
of surface processes (“space weathering”)
grain abrasion [2]
Surface processes on Itokawa
Comparison between
ü  Surface micro-morphology (µ
µCT) (Tsuchiyama+ 2011,2012)
ü  Surface nano-morphology (FE-SEM) (Matsumoto+ 2012)
ü  Rim nano-structure (TEM/STEM) (Noguchi+ 2011,2012)
ü  Noble gas isotope analysis (Nagao+ 2011)
Micrometeoroids
Space weathering
rim formation
Grain abrasion
Galactic
Solar wind
cosmi
c ray
Itokawa (rubble
pile asteroid)
Grain motion
Surface micro-morphology: Grain abrasion
Tsuchiyama+ (2011）） µCT
Particle w/ sharp edges
35/48 particles (62%)
Impact fragment
CT image
Particle w/ rounded edges
13/48 particles (38%)
External shapes also spherical
CT image
Pl
LPx
Pl
10 µm
RA-QD02-0025-2
30 µm
RA-QD02-0042
Surface micro-morphology: Grain abrasion
Tsuchiyama+ (2011）） µCT
Particle w/ sharp edges
35/48 particles (62%)
Impact fragment
Particle w/ rounded edges
13/48 particles (38%)
External shapes also spherical
CT image
CT image
Pl
LPx
Pl
abrasion
10 µm
RA-QD02-0025-2
RA-QD02-0025-2
(×
×2110)
30 µm
RA-QD02-0042
RA-QD02-0042
(×
×650)
Surface micro-morphology: Grain abrasion
Matsumoto+ (2012）） FE-SEM
Surface w/ faint steps
Surface w/ sharp steps
B0025 (cleavage steps)
B0023
abrasion
1 µm
Micro-morphology (µ
µCT)
A0017
Angular
A0049-2
Angular
A0064
Angular & Rounded
B0006
Angular & Rounded
B0023
Angular
B0025
Angular & Rounded
B0049
Angular
A0033
Rounded
Resolution
~ a few µm
100 nm
Nano-morphology (FE-SEM)
Sharp
Sharp
Sharp & Faint
Sharp & Faint
Sharp
Sharp & Faint
Sharp
Faint
~ a few 10 nm Rim nano-structure: Space weathering rim
Type-1 5 nm
Type-2 Noguchi+ (2012) STEM
Type-3 50 nm
10 nm
Thin amorphous layer Fe-rich nanoblobs in Formation of vesicles
(vapor deposition)
amorph. layer (SW He)
(blistering)
< 20 yr
Fe3+ reduced to Fe2+ > 80 yr
~103 yr
Fe3+ reduced to Fe0 Solar flare track density
Blistering (Matsumoto+ 2012)
ü  Vapor dep. (zone I) → Fe nanoblobs (zone II) → Blistering
ü  Rim depth ⇒ implantation of SW 4He+ (4 keV) (H+: 1 keV)
ü  Time scale ~103 yr. ⇔ SW Ne: 150-550 yr (Nagao+ 2011) Comparison between different structures
Sample No. Micro-morph. Nano-morph. Rim nano-str.
A0017
A
S
-
A0049-2
A
S
-
A0064
A & R
S & F -
B0006
A & R
S & F
-
B0023
A
S
-
B0025
A & R
S & F
-
B0049
A
S
-
A0033
R
F
Type 3
A0009
A
-
Type 3
A0032
R
-
Type 2
A0034
A
-
Type 1
A0041
A
-
Type 3
A0042
R
-
Type 2
A0050
A
-
Type 1
A0054
A
-
Type 2
µCT
FE-SEM
Resolution
a few µm a few 10 nm
A: angular
R: rounded
S: sharp
F: faint
STEM/TEM
~1 nm
−: not observed
Comparison between different structures
Sample No. Micro-morph. Nano-morph. Rim nano-str.
A0017
A
S
-
A0049-2
A
S
-
A0064
A & R
S & F -
B0006
A & Rrelated
-
S & F
B0023
A
S
-
B0025
A & R
S & F
-
B0049
A
S
-
A0033
R
F
Type 3
A0009
A
-
Type 3
A0032
R
-
Type 2
A0034
A
-
Type 1
A0041
A
-
Type 3
A0042
R
-
Type 2
A0050
A
-
Type 1
A0054
A
-
Type 2
µCT
FE-SEM
Resolution
a few µm a few 10 nm
A: angular
R: rounded
S: sharp
F: faint
STEM/TEM
~1 nm
−: not observed
Comparison between different structures
Sample No. Micro-morph. Nano-morph. Rim nano-str.
A0017
A
S
-
A0049-2
A
S
-
A0064
A & R
S & F -
B0006
A & R
S & F
-
B0023
A
S
-
B0025
A & R
S & F
-
B0049
A
S
-
A0033
R
F
Type 3
A0009
A
-
Type 3
A0032
R
-
Type 2
A0034
A
-
Type 1
A0041
A
-
Type 3
A0042
R
-
Type 2
A0050
A
-
Type 1
A0054
A
-
Type 2
µCT
FE-SEM
Resolution
a few µm a few 10 nm
A: angular
R: rounded
S: sharp
F: faint
STEM/TEM
~1 nm
−: not observed
Space weathering rim vs. Grain abrasion
Degree of rim formation by SW irradiation (~103 yr time scale)
Type-1 Type-2 Type-3 Particle w/
2
1
2
sharp edges
abrasion
0
2
1
Particle w/
rounded edges
ü  No relation between space weathering rim and abrasion
ü  Grain abrasion having a longer time scale
⇒ 2nd type of “space weathering” ⇒ “space erosion” Cause of “space erosion”
(a)  Mechanical abrasion by grain motion due to seismic
waves induced by small body impact (Tsuchiyama+ 2011)
Is it really possible?
ü  Experimental work
required
ü  Space weath. rim
easily abraded
Time scale
ü  <~1 My
GCR noble gas
(Nagao+ 2011)
SW ⇒ sw rim
grain motion
⇒ abrasion
seismic wave by impact of
small body (~1 cm)
(b) Sputtering by solar wind particles (probably by H+: 1 keV)
May be too short for abrasion
Two kinds of space weathering process
on the Itokawa’s surface: Summary
(1)  Formation of space weathering rim
Cause of reddening and darkening
of reflectance spectrum of asteroid
Mainly by SW irradiation (particularly He+)
Time scale: ~103 yr
（2）） Space erosion
By impact-induced grain motion(?)
Time scale: longer than (1)
<~106 yr(?)
How this process affects
larger grains?
noble gas chronology?
Similar process in lunar regolith?