““Learning about the degree of aqueous alteration of NEOs from ...

“Learning about the degree of aqueous
alteration of NEOs from laboratory IR
spectra of primitive Antarctic chondrites”
Josep M. Trigo-Rodríguez 1
&
C.E. Moyano-Cambero 1 , and J.Llorca 2
1
Institute of Space Sciences (CSIC-IEEC) Barcelona, Spain.
2 Institut de Tècniques Energètiques (UPC) Barcelona, Spain.

OUTLINE
• How biased is the available sample of Carb. Chond. (CCs)?
• We have studied a significant sample of historic falls
• The NASA Antarctic collection opportunity: rare groups
• Chondrites groups and reflectance properties in IR
• Main bands and features in IR spectra of CCs
– Recent findings on CM, CR, CI and CV groups.
– ATR spectroscopy results from 2 to 40 m
• Intrinsic chemical differences in chondrites
– Collisional effects: compaction, brecciation and aqueous alteration
• Implications for sample recovery in Marco-Polo-R
• Preliminary results
• Conclusions

WHAT WE KNOW ABOUT CARBON-RICH
RICH
ASTEROIDS FROM THEIR METEORITES?
253 Mathilde, NEAR Shoemaker (NASA)
• Chondritic meteorites are coming from
undifferentiated bodies
• 15 chondrite groups identified so far
(Weisber et al., 2006)
– Then our overall view is highly biased!
Hiroi et al. (2001)
• Chemical differences among the
chondrite groups suggest that each
group represents rocks from a different
reservoir (see e.g. Scott, 2007)
• This idea has been reinforced because
few chondrite breccias exist containing
clasts from different chondrite groups
(Bischoff et al, 2006)
• Primitive asteroidal surfaces are not
only brecciated, but also covered by
rubble (not so important for small ones)

CHONDRITE GROUPS
Weisberg et al. (2006)
• Different degrees of aqueous alteration
and metamorphism are found
• The CCs can be classified according the
estimated T required to produce the
petrographic types (Dotto et al., 2005)
• The highest hydrated groups
correspond to the carbonaceous
chondrites, particularly: CMs, CRs,
and CIs
• At the Institute of Space Sciences
(CSIC-IEEC) we work in the lab
focusing on the role of aqueous
alteration on primitive chondrites and
performing remote studies of comets
• Particularly, the reflectance spectra are
taken in the UPC Center for Research in
NanoEngineering
Dotto et al. (2005)

IR SPECTROMETER
IR BEAM SAMPLE
haz IR
Muestra
P
• Small chips of each meteorite were grinded using an agate mortar
• Powders were carefully located in between a diamond detector of a
Smart Orbit ATR (Attenuated Total Reflectance) IR spectrometer.
• This instrument provides high resolution internal reflection spectra
of meteorite powders following standard procedures and using a
diamond detector

NASA ANTARCTIC CHONDRITES
Y791198 CM2
QUE93005 CM2
Meteorite Group Weatering grade Year
ALH 77003 CO3.6 Ae 1977
ALH 83108 CO3.5 A 1983
ALH 84028 CV3 Ae 1984
EET 92159 CR2 B/C 1992
GRA 95229 CR2 A 1995
LAP 02342 CR2 A/B 2002
MAC 02606 CM2 A 2002
MET 01070 CM1 Be 2001
MET 01074 CV3 B 2001
MIL 07689 CM1 C 2007
PRE 95404 R3 A 1995
QUE 97990 CM2 Be 1997
QUE 99038 CM2 A/B 1999
QUE 99355 CM2 B 1999
SCO 06043 CM1 ~B 2006

ADDITIONAL STUDIED CHONDRITES
• Selection of historic carbonaceous chondrites, mostly well-preserved
falls, that are also included in our IR study
Meteorite Group Fall/Find Year
Allende CV3 Fall 1969
Cold Bokkeveld CM2 Fall 1838
Kainsaz CO3.2 Fall 1937
Leoville CV3 Find 1961
Mokoia CV3 Fall 1908
Murchison CM2 Fall 1969
Murray CM2 Fall 1950
Orgueil CI 1 Fall 1864

SPECTRA OF CI and CM CHONDRITES
• For the CMs several absorption bands exhibit different depths in agreement with
previous studies using IR micro-spectroscopy [e.g. Beck et al. (2010), GCA 74]
• The variable depth in OH bands at ~3 m exhibited by some of the selected CMs is
probably consequence of different degrees of aqueous alteration
Trigo-Rodríguez et al. (2012) LPSC abstract #1443

MAIN ABSORPTION BANDS
• The absorption bands identified so far are mostly due to clay minerals,
and organic features:
– Clay minerals in chondrites exhibit distinctive absorption peaks than those
shown in terrestrial clays as also was found by Beck et al. (2010)
Mineral (cm-1) (m) Notes
OH stretching hydroxyl groups 3450 2.9 Mostly all groups
(Montmorillonite,
smectite, etc...)
CC double bond stretch 1650 6.1 Organics, CMs
CH 2 & CH 3 bend bands 1450 & 1400 6.9 & 7.1 Organics, CMs
N-C libration band 1064 9.4 CO, CV
Al/Si-OH libration bands 930-950 10.8-10.5 Variable location
Al-O and Si-O, out of plane ~610 16.4 Variable location, CMs

THE KEY BANDS IN THE mid-IR
• The 3 m absorption band associated with OH hydroxyl groups is evident
for CM chondrites, but in different degrees:
– The depth of the OH bands seems to be directly related with the extent of aqueous alteration

CO and CV CHONDRITE GROUPS
• The absorption bands are also present, but in distinguishable location as
consequence of different mineralogy
• IR spectra of CO, and CV carbonaceous chondrites analyzed so far. Kainsaz,
ALH83108, and ALHA77003 are CO3 chondrites.
• Over 30 m the results should be taken with caution
Trigo-Rodriguez et al. (2012)

PRELIMINARY RESULTS
• Significant differences in the reflectance spectra of CCs reflects a
remarkable compositional diversity
– The ATR technique is very sensitive to OH and other bonds absorption bands, but
also provides information about organic features
• CC groups exhibit components with distinctive abundance ratios
– Chondrules are the abundant ingredients, but they vary in average size and
proportions, such as the Ca-Al rich inclusions (CAIs) and other components
– Metal grain abundances are highly variable from being almost absent to ubiquitous
depending of the chondrite group, and their presence inside the chondrules or in the
matrix has direct implications to reflectance
• Laboratory analyses of the reflectance of Antarctic CCs provide useful
information for remote characterization of Marco Polo-R target
– An accurate IR spectrum provides very significant features and
absorption bands that have direct application:
• The depth of the OH bands are directly related with the extent of aqueous alteration:
how much water is bounded in phyllosilicates
• The distinctive features allow to make reasonable distinction of the different surface
mineralogy (if it is a complex breccia)
• Consequently, IR spectroscopy of the target in a small scale is essential for sampling
pristine carbonaceous materials (Marco Polo-R goal)

CONCLUSIONS
• Laboratory analyses of the reflectance of Antarctic CCs provide useful
information for remote characterization of the presumably complex
surface of Marco Polo-R and Osiris-Rex missions
– IR spectra provide very significant features and absorption bands that have
direct application:
• The depth of the OH bands are directly related with the extent of aqueous alteration: how much
water is bounded in phyllosilicates
• The distinctive features allow to make reasonable distinction of the different surface
mineralogy (if it is a complex breccia)
• Consequently, IR spectroscopy of the target in a small scale is essential for sampling pristine
carbonaceous materials (Marco Polo-R goal)
– Carbon-rich asteroids are sources of all biogenic elements and have minerals
that probably synthesized complex organics (Martins, 2011):
• Some features of the most abundant organics are also identifiable by using high-res IR spectra
• We thank NASA Meteorite Working group and JSC curators for
providing us with the samples to complete these analyses.

• Marco Polo-R
Symposium:
• A symposium focusing on the
revolutionary information that
future sample return missions
can provide:
– Particularly on the
cosmochemical and
astrobiological issues, but
open to all scientific issues
concerning sample return
challenges
– Special poster session
• You are all invited to attend!
– Limited space
– Note that the workshop is
scheduled for:
• 16-17 Jan. 2013
• In the historical cloister of
the Institute for Catalan
studies (IEC)
• Near the famous Ramblas