Given the broad agreement between C, H, and O isotopic ratios in the modern atmosphere and the ALH 84001 meteorite, it is possible that these reservoirs were established after early atmospheric loss prior to 4 Ga. The preservation of these signals over this long period of history can be explained in several slightly different ways: 1) C, O, and H have remained static in the atmosphere and have not exchanged with the surface over the past 4 Ga; 2) C, O, and H in the atmosphere have potentially varied widely over history but have been continually buffered by larger reservoirs in the crust which have remained unchanged over the past 4 Ga. This second possibility allows for potentially large variations in atmospheric pressure to occur as CO2 is recycled back into the atmosphere from crustal reservoirs or degassed from the mantle

Atreya, S. K.

Christensen, L. E.

Conrad, P. G.

Flesch, G. J.

Franz, H.

Jones, J. H.

Leshin, L. A.

Mahaffy, P. R.

Manning, H.

Navarro-Gonzalez, R.

Niles, P. B.

Owen, T.

Pepin, B.

Schwenzer, S. P.

Stern, J. C.

the MSL Science Team,

Trainer, M.

Webster, C. R.

Wong, M.

NASA Technical Reports Server

PRELIMINARY INTERPRETATIONS OF ATMOSPHERIC STABLE ISOTOPES AND ARGON FROM 
MARS SCIENCE LABORATORY (SAM).  J.H. Jones1, P.B. Niles1, C.R. Webster2, P.R. Mahaffy3, G.J. Flesch2, L.E. 
Christensen2, L.A. Leshin4, H. Franz3, M. Wong5, S.K. Atreya5, P.G. Conrad3, H. Manning6, R. Navarro-Gonzalez7, T. Owen8, B. 
Pepin9, J.C. Stern3, M. Trainer3, S.P. Schwenzer10 and the MSL Science Team, 1NASA/JSC, Houston, TX 77058 
(john.h.jones@nasa.gov), 2Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Dr., Pasadena, CA 91109, 3NASA Goddard 
Space Flight Center (GSFC), Greenbelt, MD 20771, 4Rensselaer Polytechnic Institute, Troy, NY 12180, 5Univ. of Michigan, MI 
48105, 6Concordia College, Moorhead, MN, 7Universidad Nacional Autónoma de México, Mexico City, Mexico, 8Univ. of Ha-
waii, Honolulu, HI 96822, 9Univ. of Minnesota, Minneapolis, MN, 10The Open University, Milton Keynes, UK. 
 
Introduction:  The first analysis of the martian 
atmosphere was performed by the Viking missions [1, 
2]. The elevated 129Xe/132Xe ratio measured by Viking 
allowed [3] to note the similarity of the Xe extracted 
from quenched shock melts in the EETA 79001 Ant-
arctic shergottite with the Viking measurements. This 
was the first solid evidence that meteorites had been 
delivered from Mars to the Earth [3, 4].  The timing of 
this discovery was serendipitous. Only two years be-
fore, a lunar meteorite had been found in Antarctica. 
Thus, there was now solid evidence that impacts on 
other planets could deliver material to the Earth. 
In addition to the large 129Xe anomaly, Viking also 
noted that the 40Ar/36Ar of the martian atmosphere was 
~3000 and that δ15N was about +600‰  [1, 2]. Earth-
based spectroscopic measurements subsequently indi-
cated that the D/H ratio of the martian atmosphere 
(δD) was ~+4000‰ [5]. The combination of isotopi-
cally heavy N and H led to speculation that the isotopic 
composition of these elements had been modified by 
atmospheric escape processes [6]. The chemical and 
isotopic composition of the martian atmosphere was 
further refined by laboratory measurements of martian 
meteorites.  One example of this is the 40Ar/36Ar of the 
martian atmosphere, where more refined analyses of 
EET 79001 shock glasses yielded a 40Ar/36Ar ratio of 
~1900, as opposed to the Viking measurement of 
~3000 [7, 8]. Another example is that of 36Ar/38Ar = <4 
in these glasses, which is significantly lower than the 
chondritic ratio of ~5.4. This also seems to support the 
idea of preferential atmospheric loss of lighter Ar iso-
topes over geologic time [7-9].  
However, other measurements of CO2 isotopes 
have not been consistent with this atmospheric loss 
story. Viking measured δ13C and δ18O values of 0±	  
50‰. Earth-based spectroscopy has in fact suggested 
depleted values for δ13C of -22±	  20‰ [10]. Finally, the 
recent Phoenix lander measured a δ13C for CO2 in the 
martian atmosphere of -2‰ [11]. This is in contrast to 
measurements of trapped gas in martian meteorite 
EETA 79001 which yielded a δ13C of +36 ± 10‰ [12].  
Thus, a combination of robotic, laboratory, and te-
lescopic measurements have set the stage for the 
SAM/MSL analysis of the martian atmosphere. The 
SAM analyses are performed in two very different 
ways within a single instrument package:  (i) Tunable 
Laser (TLS) measurements of 18O/16O and 13C/12C in 
atmospheric CO2; and (ii) Quadrupole mass spectros-
copy (QMS) of  13C/12C, and 40Ar/36Ar.  TLS has also 
measured δD both in the Martian atmosphere and as 
evolved from a heated soil sample from Rocknest [13], 
with results currently under refinement. 
Preliminary Results:  TLS results yield an iso-
topic composition of atmospheric CO2 to be: +48±6‰ 
in δ18O and +45±4‰ for δ13C [14]. QMS results for 
δ13C are also in agreement with an average of 
+40.4±15.5‰	   [15]. These measurements agree well 
with previous δ18O results and are similar to previous 
martian meteorite measurements of δ13C. 
By QMS the 40Ar/36Ar ratio of the atmospere is 
~1900, in good agreement with martian meteorite stud-
ies [7, 8].  Refinement of this measurement is also 
underway, but it is clear that the martian atmospheric 
Ar has been highly influenced by degassing of 
radiogenic 40Ar from the crust. 
δD measurements by TLS on water in the atmos-
phere yielded values of +5000 to +7000‰ [14], in 
good agreement with both telescopic measurements 
and with a new ion probe analysis of D/H in an oli-
vine-hosted melt inclusion in the shergottite LAR 
06319 [9]. In addition δ18O of atmospheric water was 
measured at +50 ±10‰ by the TLS [14].  
Implications:  Taken at face value, our measured  
enrichments in the heavy isotopes of O, C, and H sup-
ports the paradigm of atmospheric loss processes at 
Mars. Estimates of thermal and non-thermal escape 
processes during Mars’ initial history suggest that early 
loss was catastrophic, suggesting that very little at-
mosphere survived earliest accretion and outgassing [9, 
16]. Minerals in ALH 84001 whose crystallization and 
alteration ages have been dated to be near 4 Ga contain 
our best record of these events and contain enriched C 
and H isotopes. Measurements of ALH 84001 minerals 
show δ13C ~+40‰, and δD values ~+3000‰ [17-19]. 
In this view, the δ13C and δD of the martian atmos-
phere has not changed much over about 4 Ga. This 
would also be consistent with the measurement of a 
large enrichment of δ18O in atmospheric water vapor 
which could suggest that water on Mars is not in equi-
2781.pdf44th Lunar and Planetary Science Conference (2013)
https://ntrs.nasa.gov/search.jsp?R=20130011192 2019-08-31T00:17:27+00:00Z
librium with the crust and has also been enriched in 
heavy isotopes through atmospheric loss. 
An alternate interpretation of the data suggests that 
buffering of surface volatiles by crustal reservoirs 
could play an important role in the evolution of the 
atmosphere as well as its isotopic composition.  Crustal 
reservoirs may represent a much larger volume of 
volatiles whose isotopic composition was largely es-
tablished very early. Thus, exchanges between atmos-
phere and crustal reservoirs could provide a viable 
means for preserving the fingerprint of ancient proc-
esses observed in both the ALH 84001 meteorite and 
in the modern atmosphere. 
The δ18O of martian CO2 is very heavy with respect 
to silicates in martian meteorites but is remarkably 
similar to terrestrial CO2.  Thus, this 18O enrichment 
could be a signature either of low temperature equili-
bration between water and CO2 [11] or enrichment 
through atmospheric loss. The oxygen isotopic compo-
sition of CO2 in the martian atmosphere and in carbon-
ates from martian meteorites indicate that some sort of 
buffering has indeed taken place. Jakosky and Jones 
[20] argued, based on the Viking measurement of δ18O 
~ 0‰, that oxygen could be buffered by hydrothermal 
interaction between the crust and atmosphere. The dis-
covery of extensive clay mineral formation in the an-
cient crust of Mars [21] is evidence for substantial an-
cient exchange of oxygen isotopes between water and 
the silicate crust. This buffering between crust and 
water is not indicated by our water vapor δ18O data.  
However, this might be explained by atmospheric ex-
change between CO2 and H2O with the high δ18O val-
ues being transferred from the more abundant 18O-rich 
CO2 to the less abundant water vapor.  
While the current reservoir of CO2 on Mars is 
small, ~12 mbar [22], substantial CO2 may be stored as 
carbonate in crustal materials and may be as large as 1-
3 bars [23]. The size and isotopic composition of this 
reservoir remains a large unknown. Some younger 
martian meteorites have at least trace levels of carbon-
ates with low δ13C that have been a interpreted to be 
martian [24-26], suggesting that modern carbonate 
formation is ongoing [11]. It is expected that volcanic 
degassing and carbonate precipitation should act to 
decrease the carbon isotopic composition of atmos-
pheric CO2, but exchange with an ancient, high-δ13C 
crustal reservoir may provide a means for explaining 
why δ13C has remained heavy through time.  
In contrast, the low 36Ar/38Ar from martian meteor-
ite gas probably requires loss over geologic time.  If 
the escape modeling is correct, minor gases like N, Ne, 
and Ar were totally removed following atmospheric 
collapse near 4 Ga and then replaced by later out-
gassing of the martian interior.  It is expected that de-
gassed 36Ar/38Ar was initially chondritic/solar and then 
that ratio became sub-chondritic as 36Ar was preferen-
tially lost [6].  The enriched 15N signature of the at-
mosphere is also attributed to this process. 
Summary: Given the broad agreement between C, 
H, and O isotopic ratios in the modern atmosphere and 
the ALH 84001 meteorite, it is possible that these res-
ervoirs were established after early atmospheric loss 
prior to 4 Ga. The preservation of these signals over 
this long period of history can be explained in several 
slightly different ways: 1) C, O, and H have remained 
static in the atmosphere and have not exchanged with 
the surface over the past 4 Ga; 2) C, O, and H in the 
atmosphere have potentially varied widely over history 
but have been continually buffered by larger reservoirs 
in the crust which have remained unchanged over the 
past 4 Ga. This second possiblility allows for poten-
tially large variations in atmospheric pressure to occur 
as CO2 is recycled back into the atmosphere from 
crustal reservoirs or degassed from the mantle. 
Future Work:  A planned SAM experiment that 
concentrates minor atmospheric constitutents may al-
low the measurement of the isotopic compositions of 
N2, 38Ar, Kr and Xe. Measurement of those isotopes 
that are most easily influenced by spallation and n-
capture would allow determination of the influence of 
impact vaporization processes on the martian atmos-
phere.  In particular, the abundances of 80Kr, 82Kr, 
124Xe, and 126Xe should be especially sensitive to cos-
mogenic production in the martian crust. 
References: 1. McElroy M.B., et al. (1976) Science, 194, 
1295-1298. 2. Nier A.O., et al. (1976) Science, 194, 68-70. 3. 
Bogard D.D. and Johnson P. (1983) Science, 221, 651-654. 
4. Pepin R.O. (1985) Nature, 317, 473-475. 5. Krasnopolsky 
V.A., et al. (1998) Science, 280, 1576-1580. 6. McElroy 
M.B., et al. (1976) Science, 194, 70-72. 7. Garrison D.H. and 
Bogard D.D. (1998) Meteoritics & Planetary Science, 33, 
721-736. 8. Garrison D. and Bogard D. (2000) Meteoritics 
and Planetary Science Supplement, 35, 58. 9. Pepin R.O. 
(1994) Icarus, 111, 289-304. 10. Krasnopolsky V.A., et al. 
(2007) Icarus, 192, 396-403. 11. Niles P.B., et al. (2010) 
Science, 329, 1334-1337. 12. Carr R.H., et al. (1985) Nature, 
314, 248-250. 13. Leshin L., et al. (2013) LPSC. 14. Webster 
C.R. et al. (2013) LPSC. 15. Franz H., et al. (2013) LPSC. 
16. Lammer H., et al. (2012) Space Science Reviews, 1-42. 
17. Leshin L.A., et al. (1996) Geochimica et Cosmochimica 
Acta, 60, 2635-2650. 18. Greenwood J.P., et al. (2008) 
Geophysical Research Letters, 35, 05203. 19. Romanek C.S., 
et al. (1994) Nature, 372, 655-657. 20. Jakosky B.M. and 
Jones J.H. (1994) Nature, 370, 328-329. 21. Bibring J.P., et 
al. (2006) Science, 312, 400-404. 22. Phillips R.J., et al. 
(2011) Science. 23. Bandfield J.L., et al. (2003) Science, 301, 
1084-1087. 24. Clayton R.N. and Mayeda T.K. (1988) 
Geochimica et Cosmochimica Acta, 52, 925-927. 25. Jull 
A.J.T., et al. (1997) Journal of Geophysical Research-
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Geochimica Et Cosmochimica Acta, 56, 817-826.  
2781.pdf44th Lunar and Planetary Science Conference (2013)


Preliminary Interpretations of Atmospheric Stable Isotopes and Argon from Mars Science Laboratory (SAM)

the MSL Science Team

Open Research Online (The Open University)

English

Preliminary interpretations of atmospheric stable isotopes and argon from Mars Science Laboratory (SAM)

Preliminary Interpretations of Atmospheric Stable Isotopes and Argon from Mars Science Laboratory (SAM)

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