martian atmospheric and interior volatiles in the meteorite nakhla

Martian atmospheric and interior volatiles in the meteoriteNakhla

K.J. Mathew �, K. MartiDepartment of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0317, USA

Received 7 June 2001; received in revised form 27 February 2002; accepted 28 February 2002

Abstract

We report isotopic abundances of xenon, argon, and nitrogen for the observed distinct components in Martianmeteorite Nakhla. In a stepwise release the 129Xe/132Xe ratios in the 800‡C and 1000‡C fractions show the signature ofthe modern atmosphere and other Xe ratios, when corrected for the cosmogenic component, confirm the isotopicallyfractionated modern atmospheric component. On the other hand, the Xe isotope ratios in the s 1000‡C steps revealan isotopically unfractionated interior component, but with radiogenic 129Xe excesses. The isotopic composition ofthis interior component is consistent with Chass-S Xe (solar type), but is augmented by 244Pu-derived fission Xe. Thefission components in interior trapped Xe (in both Nakhla and Chassigny) suggest that Mars effectively retained244Pu-derived fission gas. A heavy (relative to interior N) nitrogen signature in the 600^900‡C temperature steps alsosuggests a recent incorporation of Martian atmospheric gases. The N signatures in the high-temperature (s 1000‡C)steps are strongly affected by cosmic-ray-produced 15Nc and 36Ar and 38Ar abundances are dominated by thecosmogenic component. We discuss the signatures of Martian interior nitrogen and heavy noble gases and theconstraints they provide on the evolutionary history of Mars. ß 2002 Elsevier Science B.V. All rights reserved.

Keywords: Mars; SNC meteorites; volatiles; atmosphere; nitrogen; noble gases

1. Introduction

It is now generally accepted that the SNC (sher-gottites, nakhlites, and Chassigny) meteoriteshave a Martian origin [1], and their volatiles pro-vide important information regarding the evolu-tion of the planet. The gases in shock-meltedglasses of shergottites provide nitrogen, argonand xenon isotopic signatures that agree with

those measured by the Viking spacecraft. Thepresence of a modern atmospheric component re-veals recent exchanges with the Martian atmo-sphere. Since the chronologies of nakhlites di¡erfrom those of shergottites and ALH84001 [2^4],the components acquired at di¡erent times mayprovide insights into the evolutionary history ofthe planet. Among several isotopic markers aspotential tracers, the ratios 15N/14N, 129Xe/132Xeand 40Ar/36Ar show the largest variations andshould prove useful in disentangling the distinctcomponents in SNC meteorites [5^10].

The shergottites with young radiometric ages[2] may be best suited to study recently introduced

0012-821X / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved.PII: S 0 0 1 2 - 8 2 1 X ( 0 2 ) 0 0 5 6 2 - 9

* Corresponding author. Tel. : +1-858-534-0443;Fax: +1-858-534-7441.

E-mail address: [email protected] (K.J. Mathew).

EPSL 6189 26-4-02

Earth and Planetary Science Letters 199 (2002) 7^20

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Martian atmospheric gases, while the apparentlyancient atmospheric component in ALH84001[10^12] is not only distinct from the modern com-ponents in shergottites, but also di¡ers from theinterior volatile reservoir sampled by Chassigny[12]. Previous work on Nakhla revealed a spalla-tion component [13], a trapped atmospheric com-ponent with high 129Xe/132Xe [9,14^17], and lowerKr/Xe elemental ratio than in the modern atmo-spheric component. This was interpreted to be theresult of aqueous alteration in the formation ofiddingsite [15,18]. On the other hand, the work ofGilmour et al. [16,17] showed that an atmosphericXe component is observed close to the grainboundaries and is associated with leachable io-dine, indicating a shock incorporation of ad-sorbed atmospheric gases.

The present study of Nakhla aims to bettercharacterize the interior volatile components inorder to study the relationships between atmo-spheric and interior components.

2. Experimental procedures

A bulk sample Nakhla C was provided by theNatural History Museum, London, UK, and wasused for a pilot sample (Nakhla C,01) to deter-mine temperature cuts for a high-resolution studyof nitrogen and noble gas components in NakhlaC,02. A small clast (Nakhla C,11) of di¡erentappearance was also selected.

The Nakhla samples were step-heated by anexternal resistance heater up to 1100‡C in a dou-ble-walled quartz system within a separatelypumped vacuum jacket and then transferred invacuo into an Mo crucible, mounted in a dou-ble-walled quartz system, for step-heating by ra-dio frequency to the melting temperatures. N andnoble gases were analyzed in the static mode witha magnetic-sector mass spectrometer equippedwith a Baur-Signer ion source. Xe is separatedfrom Ar and N by adsorption on a glass ¢ngerat liquid N2 temperature [19]. A volume split isused for the measurement of the N isotopic com-position and abundances. The remaining fractionis used for measurement of the Ar isotopes. Arand Xe from several steps are combined to im-

prove measurement statistics. Extraction blankmeasurements were carried out between runs,and the sensitivity was monitored using pipets ofair standards and was found to be constant (with-in 5%) during the entire set of runs. Data arecorrected for system blanks, mass spectrometerbackground, and instrumental mass discrimina-tion. An instrumental mass discrimination forXe of 0.18% per amu favoring the light isotopeswas determined and for nitrogen the discrimina-tion was corrected according to calibrations withair pipets, details of the experimental proceduresemployed were given earlier [20,21]. The extrac-tion blanks for N were 0.2^0.4 ng N for the9 1400‡C steps and were consistent with atmo-spheric in composition (N15N = 0 þ 3x). Typicalblanks for 36Ar and 132Xe were 3^6U10312 cm3

STP and 1^2U10314 cm3 STP, respectively.The uncertainties in concentrations include

those in the reproducibility of the N and noblegas standards (V5% for N, Ar, and Xe abundan-ces; isotopic signatures are reported at 95% con-¢dence limits). The propagated uncertainties inthe isotopic ratios include statistical errors, uncer-tainties in the mass discrimination, and in theblank corrections.

3. Identi¢cation of Martian xenon components inNakhla

3.1. Spallation Xe

The measured Xe isotopic abundances in high-temperature steps (see Background Data Set1) re-veal signi¢cant spallation components on the lightisotopes. In order to facilitate the resolution ofthe individual trapped components, the measuredXe isotopic data are ¢rst corrected for the cosmo-genic component. We follow procedures describedby Mathew et al. [22], which use partitioningbased on the measured 126Xe/130Xe ratio.

The spallation Xe systematics have been exten-sively studied in lunar samples and in meteorites,and it is known that relative spallation yields de-

1 http://www.elsevier.com/locate/epsl

EPSL 6189 26-4-02

K.J. Mathew, K. Marti / Earth and Planetary Science Letters 199 (2002) 7^208

pend on the shielding depth and on the chemicalcomposition, speci¢cally the Ba/REE ratio (e.g.Marti and Lugmair [23]). Spallation spectra forNakhla and Lafayette were also reported (Roweet al. [13]), but the uncertainties are large. For adetailed assessment of trapped components, it isimportant to obtain precise relative spallationyields from the Nakhla data set (see the Back-ground Data Set1). Two properties of the trappedXe components in Nakhla, which will be furtherdiscussed later, allow an evaluation of the spalla-tion records. First, the ¢ssion Xe component inthe high-temperature (s 1000‡C) fractions ofNakhla is well mixed with Martian interior Xe,and the two components are released as a homo-geneous ‘evolved trapped’ Xe component. Second,the stepwise release patterns of spallation Xe andof ‘evolved trapped’ Xe di¡er, permitting the eval-uation of spallation Xe spectra by comparing(subtracting) temperature fractions of NakhlaC,02 and Nakhla C,01 (data using Nakhla C,11give consistent results but uncertainties are larg-er). We adopt the following relative spallationyields and uncertainties : 124Xe: 126Xe: 128Xe:130Xe: 131Xe: 132Xe: 134Xe = 0.606 þ 0.003:r1.00:1.45 þ 0.03: 0.93 þ 0.06: 2.6 þ 0.3: 0.85 þ 0.25:0.28 þ 0.11. The size of spallation correctionsand related uncertainties due to the correctionof spallation components are given in Table 1and are further elaborated in Table 1 footnotes.

In contrast to Chassigny and ALH84001, wherethe spallation components were in part released inthe 6 600‡C temperature steps [12], the spallationXe signature in Nakhla is observed only in thev 800‡C steps. The calculated spallation 126Xes

concentration of 6.6 þ 0.2U10313 cm3 STP/g(1c) in the three Nakhla samples is consistentwith values reported by Ott [9] and Gilmour etal. [16]. The relatively small ratio (131Xe/126Xe)c

in Nakhla reveals a cosmic-ray exposure geometrywith low shielding.

3.2. Modern atmospheric xenon

The 129Xe/132Xe ratios in the temperature frac-tions of all three samples show large variations(Table 1), as previously noted by Ott [9].Although bulk 129Xe/132Xe ratios in Nakhla are

comparable to those reported in ALH84001, thehighest measured 129Xe/132Xe ratios are distinct(2.40 þ 0.04 in Nakhla vs. 2.20 þ 0.04 inALH84001 [9,10,12,14^17,24^27]). While 129Xeexcesses in Nakhla C,01 and C,02 of V6U10312

and 9U10312 cm3 STP/g (in relation to 129Xe/132Xe = 1.08 þ 0.006 in Chass-S [12]) are consistentwith reported 129Xe excesses of 7^11U10312 cm3

STP/g in the unirradiated ‘dry samples’ of Gil-mour et al. [16], only one of the three bulk sam-ples reported by Ott [9] had comparable 129Xeexcesses. These records indicate variable mixturesof components. We discuss the resolution of dis-tinct ‘trapped’ Xe components, using the system-atics of ratios 129Xe/132Xe vs. 136Xe/132Xe (Fig. 1).For reference, Ott’s data (two steps) are includedin Figs. 1 and 3.

The (Nakhla C,02) low-temperature data (Ta-ble 1 and Fig. 1) show that Xe isotopic data inthe 9 300‡C extraction steps is similar to terres-trial atmospheric Xe (V3% of the total 132Xe isreleased in these steps) and apparently representsterrestrial atmospheric contamination. Xenon inthe 400^500‡C fractions (V4% of total 132Xe)plots close to ‘Chass-E’ [12], but some contribu-tion from adsorbed terrestrial atmospheric Xecannot be excluded. The 800‡C and 1000‡C dataof Nakhla plot close to the signature ‘Mars Atm’which represents the atmospheric Xe component,which is well documented in shock-melted glass inshergottites. We note that Xe in the 600‡C extrac-tion apparently also contains some atmosphericXe, and a fraction of 1200‡C step may also con-tain some Xe with the ‘Mars Atm’ signature, asjudged from the 129Xe/132Xe ratio.

A disentangling of the Martian atmospheric Xecomponent is achieved by characteristically high129Xe/132Xe ratios. However, Fig. 1 also illustratesthat the large shifts in the 136Xe/132Xe ratio can-not be explained simply by a ‘Mars Atm’ compo-nent, but reveal a ¢ssion Xe signature. Before weaddress the ¢ssion signature, we compare (Fig. 2)the Martian atmospheric Xe component in Nakh-la with the reported modern atmospheric data inglass of shergottites [22,28]. For Nakhla we ob-tain the following concentration weighted averagefor the 800‡C and 1000‡C Xe temperature steps(data from Table 1): 124Xe: 126Xe: 128Xe: 129Xe:

EPSL 6189 26-4-02

K.J. Mathew, K. Marti / Earth and Planetary Science Letters 199 (2002) 7^20 9

Tab

le1

Spal

lati

on-c

orre

cted

Xe

isot

opic

rati

osin

Nak

hla

Sam

ple

T13

2X

e12

6X

ea c12

4X

e/13

6X

e12

8X

e/13

6X

e12

9X

e/13

6X

e13

0X

e/13

6X

e13

1X

e/13

6X

e13

2X

e/13

6X

e13

4X

e/13

6X

e(‡

C)

Nak

hla

C,0

1,11

2m

g40

00.

110

002.

40.

170.

0095

þ38

0.21

69þ

786.

512

þ10

10.

4530

þ69

2.32

4þ

312.

902

þ30

1.14

5þ

1212

002.

10.

210.

0087

þ39

(12)

b0.

2199

þ87

(83)

4.55

2þ

920.

4383

þ63

(111

)2.

267

þ31

(58)

2.82

0þ

28(5

5)1.

154

þ12

(22)

1550

6.6

0.29

0.00

91þ

33(5

)b0.

2168

þ80

(36)

3.62

0þ

740.

4222

þ69

(49)

2.17

4þ

26(2

5)2.

754

þ25

(24)

1.14

0þ

12(1

0)T

otal

c11

.10.

670.

0091

þ35

(10)

b0.

2174

þ81

(50)

4.39

9þ

830.

4317

þ68

(67)

2.22

3þ

28(3

5)2.

798

þ27

(32)

1.14

4þ

12(1

3)N

akhl

aC

,02,

457

mg

250

0.17

70.

0000

0.00

91þ

180.

2136

þ45

3.05

6þ

260.

4629

þ55

2.38

6þ

243.

029

þ31

1.16

9þ

1230

00.

231

0.00

010.

012

þ24

0.21

73þ

333.

234

þ23

0.46

22þ

492.

435

þ30

3.04

0þ

301.

171

þ17

400

0.23

80.

0001

0.01

31þ

160.

2632

þ44

3.31

7þ

290.

5018

þ54

2.46

3þ

323.

153

þ43

1.19

5þ

1650

00.

252

0.00

010.

0121

þ19

0.26

11þ

473.

327

þ26

0.50

80þ

602.

457

þ28

3.14

1þ

401.

199

þ15

600

0.25

20.

0001

0.01

13þ

190.

2444

þ43

4.19

2þ

270.

4983

þ59

2.42

2þ

313.

096

þ45

1.18

2þ

1780

01.

770

0.06

920.

0092

þ17

0.20

88þ

406.

887

þ51

0.44

29þ

432.

285

þ18

2.86

9þ

191.

134

þ8

1000

1.40

20.

0906

0.00

95þ

230.

2126

þ49

6.77

0þ

660.

4480

þ49

2.29

8þ

192.

888

þ21

1.14

1þ

812

004.

445

0.20

030.

0090

þ25

(5)b

0.22

06þ

50(3

9)4.

861

þ34

0.43

09þ

47(5

0)2.

226

þ18

(26)

2.80

3þ

16(2

5)1.

156

þ7(

10)

1550

3.88

20.

2765

0.00

89þ

28(8

)b0.

2213

þ58

(59)

3.76

0þ

330.

4269

þ47

(78)

2.20

7þ

18(4

2)2.

784

þ19

(39)

1.15

7þ

8(16

)T

otal

12.6

50.

637

0.00

93þ

24(7

)b0.

2200

þ50

(43)

4.88

7þ

390.

4379

þ47

(57)

2.25

4þ

19(3

0)2.

840

þ20

(28)

1.15

4þ

8(11

)N

akhl

aC

,11,

59m

g50

00.

110

001.

60.

190.

0090

þ50

0.21

89þ

055.

314

þ10

50.

4681

þ93

2.40

2þ

362.

954

þ36

1.15

7þ

415

509.

70.

470.

0092

þ53

(6)c

0.21

09þ

08(4

0)3.

858

þ11

90.

4292

þ97

(54)

2.21

8þ

31(2

9)2.

789

þ30

(27)

1.14

1þ

2(11

)T

otal

c11

.30.

660.

0091

þ53

(10)

b0.

2119

þ07

(49)

4.05

5þ

117

0.43

44þ

97(6

5)2.

242

þ32

(34)

2.81

1þ

31(3

3)1.

143

þ3(

13)

The

132X

ean

d12

6X

e cco

ncen

trat

ions

are

inun

its

103

12cm

3ST

P/g

.aP

arti

tion

ing

at12

6X

eis

sele

cted

,ac

cord

ing

tosi

gnat

ure

oftr

appe

dX

e.T

he12

6X

e/13

6X

era

tio

oftr

appe

dX

eis

cons

iste

ntw

ith

Cha

ss-E

for

the

400^

600‡

Cst

eps,

(mod

ern)

Mar

tian

atm

osph

eric

for

the

800

and

1000

‡Cst

eps,

and

mix

ture

ofC

hass

igny

and

¢ssi

onX

efo

rth

e12

00an

d15

50‡C

step

s.Se

lect

edsp

alla

tion

Xe

data

124X

e12

6X

e12

8X

e13

0X

e13

1X

e13

2X

e13

4X

eSe

t1

(C,0

2,15

50‡C

,C

,01,

1550

‡C)

0.60

3=

1.00

1.48

0.96

2.82

1.00

0.39

Set

2(C

,02,

1200

‡Can

d15

50‡C

)0.

605

=1.

001.

450.

872.

300.

60.

26Se

t3

(C,0

2,12

00‡C

(=70

%in

teri

or,

30%

atm

)an

d15

50‡C

)0.

609

=1.

001.

420.

962.

660.

960.

19

Ado

pted

spec

tra

(ave

rage

)ra

nge

0.60

6=

1.00

1.45

0.93

2.59

0.85

0.28

þ0.

003

0.03

0.06

0.3

0.25

0.11

Thi

sad

opte

dsp

alla

tion

spec

trum

isco

nsis

tent

wit

hth

atof

Row

eet

al.

[13]

(Nak

hla

and

Laf

ayet

te),

wit

hin

thei

rla

rge

unce

rtai

ntie

s,an

dag

rees

wit

hth

esi

licat

esp

alla

tion

spec

tra

ofP

epin

etal

.[4

4]fr

omlu

nar

sam

ples

(exc

ept

for

131X

e/12

6X

e),

and

wit

hth

eM

arti

etal

.[4

5](S

tann

ern)

data

.T

hesp

alla

tion

corr

ecti

ons

inN

akhl

aC

,02

are

3%at

134X

e,4%

at13

2X

e,15

%at

131X

e,24

%at

130X

e,4%

at12

9X

e,48

%at

128X

e,93

%at

126X

e,an

d89

%at

124X

e,w

ith

the

follo

win

gra

nges

:13

4X

e(2

.4^4

%),

132X

e(3

.4^6

%),

131X

e(1

2^20

%),

130X

e(2

0^31

%),

129X

e(2

.4^7

.3%

),12

8X

e(4

4^57

%),

126X

e(9

2^95

%)

and

124X

e(8

7^92

%)

(Cor

rect

ions

inth

e80

0an

d12

00‡C

step

sar

eat

the

low

end

and

thos

efo

r10

00an

d15

50‡C

onth

ehi

ghen

d).

bT

heen

trie

sin

pare

nthe

ses

corr

espo

ndto

addi

tion

alun

cert

aint

ies

due

toth

eco

rrec

tion

ofth

esp

alla

tion

Xe

usin

gsp

ectr

alis

ted

abov

e.c T

otal

132X

ein

Nak

hla

sam

ples

C,0

1an

dC

,11

dono

tin

clud

eth

elo

wes

tte

mpe

ratu

rere

leas

e(6

1%of

the

tota

l)th

atha

dis

otop

icco

mpo

siti

onco

nsis

tent

wit

hte

r-re

stri

alat

mos

pher

icX

e.U

ncer

tain

ties

liste

dar

eth

ose

inth

ele

ast

sign

i¢ca

nt¢g

ures

ofth

eis

otop

icra

tios

(2c

).

EPSL 6189 26-4-02


130Xe: 131Xe: 132Xe: 134Xe: 136Xe = 0.0227 þ0.0045:r0.021: 0.4728 þ 0.0093: 15.57 þ 0.13:r1.00: 5.130 þ 0.042: 6.521 þ 0.42: 2.59 þ 0.018:2.278 þ 0.015. These ‘Nakhla atmospheric’ dataare in excellent agreement with modern Martianatmospheric Xe [22] (the zero line in Fig. 2). Gil-mour et al. [16] inferred that trapped Xe in Nakh-

la is entirely consistent with modern atmosphericXe on the basis of correlation plots of isotopicratios. For comparison, the SPB (Shergotty-par-ent-body) Xe composition derived by Swindle etal. [28] from glasses in EET79001 and the atmo-spheric Xe signatures derived by Gilmour et al.[16] from Nakhla are shown.

3.3. Interior xenon

The ratio 129Xe/132Xe = 2.40 (Table 1, Fig. 1) isnot the only signature which identi¢es a modernatmospheric component in the 800‡C and 1000‡Csteps of Nakhla C,02. Fig. 3 shows that also theratios 128Xe/136Xe, 130Xe/136Xe, and 132Xe/136Xeagree with ‘Mars Atm’ data, while data of the400^600‡C fractions show an additional interiorcomponent, consistent with Chass-S Xe ( = 124Xe:126Xe: 128Xe: 129Xe: 130Xe: 131Xe: 132Xe: 134Xe:

Fig. 2. Deviations (in per mil) of the ‘atmospheric compo-nent’ in Nakhla (weighted average of the 800 and 1000‡Csteps, corrected for spallation component) from the signatureof modern atmospheric Xe in shergottites [22] (zero line).For comparison, the data of SPB Xe reported by Swindle etal. [28] and the atmospheric composition derived by Gilmouret al. [16] are also shown (mass numbers are o¡set).

Fig. 1. The modern atmospheric component is shown in theplot of the spallation-corrected 129Xe/132Xe vs. 136Xe/132Xeratios. The 400‡C and 500‡C extractions of Nakhla C,02(right-¢lled circles) have Xe signatures consistent with Chass-E Xe (the interior Xe component observed in Chassigny)while the 250 and 300‡C steps (open circles) apparently rep-resent adsorbed terrestrial Xe (contamination). The 800^1000‡C data (top-¢lled circles) are consistent with the mod-ern Martian atmospheric Xe and the 600‡C datum falls be-tween Chass-E Xe and Martian atmospheric Xe. Expectedshifts due to ¢ssion component and due to radiogenic 129Xeare indicated. Isotopic data in the s 1000‡C steps (¢lledsymbols in Figs. 1 and 3) reveal a ¢ssion component. Mars‘early’ Atm is the Xe composition inferred for ancient atmo-spheric Xe [12], Chass-S denotes solar-type primitive interiorXe of Mars and Chass-E represents evolved interior Xe inChassigny [12], ALH84-HT represents the high-temperaturesteps of ALH84001 [12], and SW is the solar wind Xe com-position determined in lunar ilmenites [43]. Xenon data oftwo Nakhla samples reported by Ott [9] are included forcomparison. The numbers assigned to symbols represent ex-traction temperature (in 100‡C).

EPSL 6189 26-4-02


136Xe = 0.0048: 0.0043: 0.0846: 1.08: 0.1656:0.8243: 1.00: 0.3650: 0.2982 [12]). The xenondata in the s 1000‡C temperature steps, on theother hand, show not only much lower 129Xe/132Xe ratios (Table 1, Fig. 1), but also that otherXe ratios are characterized by trapped Chass-Sand ¢ssion Xe isotopic signatures. The data(Fig. 3) plot on a mixing-line of componentsChass-S and ¢ssion Xe, due to extinct 244Pu (bot-tom panel). The trapped Xe isotopic composition

is very uniform in all high-temperature steps ofthe three Nakhla samples, re£ecting a well-mixedinterior reservoir, initially made up of Chass-S Xe[12] and 244Pu-derived ¢ssion Xe. In fact, the uni-form mixture of trapped Xe and ¢ssion Xe haspermitted the resolution of the spallation Xe com-ponent, as discussed earlier. Note that in Fig. 3the s 1000‡C temperature steps of ALH84001(ALH84-HT) also plot on the Chass-S and244Pu-¢ssion tie-line. We can now calculate theamount of ¢ssion Xe that was added in the sourceregion of Nakhla, based on the isotopic shifts rel-ative to Chass-S Xe, and we obtain136Xef = 7U10313 cm3 STP/g. This may be com-pared to Ott’s [9] reported lower limit ofV2U10313 cm3 STP/g in the 1600‡C release.The U abundance in Nakhla [29] yields an insitu produced ¢ssion Xe component of 3^4U10314 cm3 STP/g during 1.3 Ga, which missesthe amount required by the data for the Nakhlasource region by a factor of V16. Of course, alsothe observed ¢ssion signature (Fig. 3) identi¢es244Pu as the precursor. The trapped Xe compo-nent in the high-temperature (s 1000‡C) data ofNakhla reveals an accumulation of a ¢ssion Xecomponent which was produced very early inMartian history by the decay of 244Pu and wasretained in the interior of Mars. The inferred ¢s-sion excesses and the 129Xe excesses in Nakhla(compared to Chass-S) yield a 129Xer/136Xef ratioof V6 (for s 1000‡C temperature steps).

We now explore (Fig. 4) a few of the correla-tions which were used by Gilmour et al. [16] toresolve distinct Xe components in Martian mete-orites, speci¢cally the measured 124Xe/131Xe vs.129Xe/131Xe and vs. 132Xe/131Xe ratios. The lowerpanel of Fig. 4 shows that our data (see the Back-ground Data Set1) are consistent with a linearcorrelation between a ‘spallation-free’, but other-wise ill-de¢ned trapped component, and in situproduced spallation Xe. In order to compareour data with those of Gilmour et al. [16], wehave included in the upper panel of Fig. 4 dottedlines that indicate mixing lines of a Martian at-mospheric Xe component with Chass-S Xe andair (terrestrial contamination), or with spallationXe. The Nakhla, 02 data (¢lled symbols in Fig. 4)and the corresponding spallation-corrected data

Fig. 3. A ¢ssion component in Nakhla is inferred from thecorrelation 128Xe/136Xe vs. 130Xe/136Xe (upper panel) and thesignature of the ¢ssion gas from the correlation 128Xe/136Xevs. 132Xe/136Xe (lower panel). Data are corrected for spalla-tion Xe, following procedures discussed in text. These twoplots permit the resolution of the Xe components discussedin text: solar-type, terrestrial (contamination), 244Pu ¢ssion,and Martian atmospheric components. The 800 and 1000‡Csteps of Nakhla C,02 (top-¢lled circles) are consistent withmodern Martian atmospheric Xe and the s 1000‡C steps(¢lled circles) are consistent with interior Xe modi¢ed by as-similated ¢ssion components. For the high-temperature stepsof Nakhla C,02, error ellipses (major and minor axes aremarked by arrows) include the propagated uncertainties in-volved in the correction of spallation Xe. See Fig. 1 forreference isotopic compositions.

EPSL 6189 26-4-02


(from Table 1, open symbols in Fig. 4) are con-nected by broken lines. The corrected data ploto¡ the tie-line Mars^Earth atmospheres and dem-onstrate the presence of a ¢ssion Xe component,which was not considered in the data analysis ofGilmour et al. [16]. It appears that both data setsare consistent, but as a result of the exclusion ofthe ¢ssion component, the interpretations by Gil-mour et al. [16] di¡er.

The Nakhla data do not permit the identi¢ca-tion of a ¢ssion-free ‘Chass-S’ component, whichwas observed prominently in the low-temperaturedata of Chassigny [12] and apparently representsan unevolved sample of interior volatiles. Thissuggests that the source regions of these two me-teorites are not identical.

In contrast to the trapped Xe component in thehigh-temperature data which reveal a well-mixedsystem, the step-heating data of Nakhla show thatthe atmospheric component in the 800‡C and1000‡C has not been mixed with the high-temper-ature component. The time of incorporation ofthe modern atmospheric Xe cannot further beconstrained by the Xe data. For possible chrono-logical hints, we turn to the Ar data.

4. Argon: atmospheric, radiogenic, and spallationcomponents

The isotopic data of Ar in individual temper-ature steps are expected to represent mixtures oftrapped components, radiogenic Ar from in situdecay of 40K, as well as spallation 36Arc and 38Arc

produced during cosmic-ray exposure. The mea-sured 40Ar abundances in Nakhla 01 and 02 (Ta-ble 2) agree within 5% with each other and alsowith those reported by Ott [9].

The ratios 40Ar/36Ar and 36Ar/38Ar in the9 400‡C steps suggest a terrestrial atmosphericcontamination, but the abundances in these stepsare small and amount to 6 2x of the total 40Ar.The radiogenic component is observed in all tem-perature steps s 500‡C and for the three Nakhlasamples an average 40Ar = 7.37 þ 0.23U1036 cm3

STP/g (1c) is calculated, which is consistent withradiogenic 40Ar expected from decay of 40K in 1.3Ga (K2O reported from 0.1^0.166% [29]).

The 36Ar and 38Ar inventories are dominatedby the spallation component, which accountsfor s 93% of the total 36Ar. The trapped 36Arconcentrations (Table 2) are obtained by compo-nent separation, using (36Ar/38Ar)c = 0.65 in thespallation component and trapped Ar with signa-tures (36Ar/38Ar)Atm = 4.1 þ 0.2 [7], adopted for themodern atmospheric component, and v 5.2,adopted for interior Ar [12]. Low shielding is in-

Fig. 4. Measured ratios (¢lled symbols) 132Xe/131Xe vs.124Xe/131Xe are shown (lower panel) as well as ratios 129Xe/131Xe vs. 136Xe/131Xe (upper panel). The spallation-correcteddata (open symbols) from Table 1 (renormalized) are alsoplotted. For Nakhla C,02 the measured and corrected dataare joined by dashed line, indicating the shifts due to thespallation correction. The (spallation-free) trapped Xe com-position (lower panel) cannot be constrained. Dotted lines inupper panel show two-component mixing lines of Martianatmospheric Xe with solar-type Xe (Chass-S), air (contamina-tion) and spallation xenon, respectively. Expected shifts dueto spallation and ¢ssion components are indicated in theupper panel; also spallation data (solid arrows) inferred byGilmour et al. [16] are shown.

EPSL 6189 26-4-02


dicated by the 131Xe/126Xe spallation ratio and weuse the spallation 36Ar/38Ar ratio of 0.65 adoptedby Bogard [31], which is consistent with valuesinferred for Chassigny and Shergotty (Ott [9]).However, we note that a change in the trappedAr composition from the adopted value of 4.1 toeither 3.5 [31] or 5.3 (interior Ar component inChassigny [12]) changes the elemental abundanceratio 36Ar/132Xe by 6 5%, while a 3% uncertaintyin the assumed spallation Ar ratio changes thiscomponent by V30%.

The concentration 38Arc = 1.95 þ 0.09U1038

cm3 STP/g (1c) is consistent with a value1.80 þ 0.16U1038 cm3 STP/g reported by Ott [9](averages of three Nakhla samples in both cases).Thus cosmic-ray exposure ages consistent withliterature data (also consistent with those of Chas-signy) are obtained. Consistent cosmic-ray expo-sure ages of Chassigny and Nakhla were taken toindicate that both may have been ejected in thesame cratering event, also the radiometric chro-nologies are similar [2,30].

As discussed earlier, Xe data in the 800‡C and

1000‡C steps indicate a modern Martian atmo-spheric component. Therefore, we consider thepossibility that also a Martian atmospheric Arcomponent is present. A calculation based on132Xe abundances in the 800‡C and 1000‡C stepsand ratios 40Ar/36Ar and 36Ar/132Xe for atmo-spheric gases of 1900 and 900 [31,32], respectively,predict an atmospheric 40Ar component of5U1036 cm3 STP/g, which is V70% of the mea-sured 40Ar abundance in Nakhla. This calculationshows that although some 40Ar of atmosphericorigin may be present, the process of incorpora-tion must have strongly discriminated against Ar.We note that also the 36Ar/132Xe ratio in Nakhla(Table 2) is lower by an order of magnitude whencompared to the modern atmospheric gases.

We have ignored in the discussion so far, apossible contribution by an interior 40Ar compo-nent, but this contribution may be estimated fromChassigny data. The solar-type Xe component inNakhla and the 40Ar/132Xe ratio in Chassigny pre-dict a ‘Chassigny-type’ interior 40Ar abundancesof only V1% of the measured 40Ar abundances.

Table 2Measured 36Ar concentrations and Ar isotopic ratios (95% con¢dence limits) in Nakhla

Sample T 36Ar 40Ar/36Ar 36Ar/38Ar 40Ar 36Art132Xet

129Xe/132Xe 36Ar/132Xe 84Kr/132Xe(‡C)

Nakhla C,01,112 mg

9 400 0.08 280 þ 30 5.20 þ 0.15 ^ 0.1 1.020 ^ 3.5 þ 0.51000 5.20 11610 þ 120 1.14 þ 0.03 60372 2.55 2.4 2.260 106 þ 15 4.2 þ 0.41200 19.99 350 þ 4 0.71 þ 0.02 6997 1.37 2.1 1.630 65 þ 16 4.1 þ 0.41550 115.96 40 þ 2 0.69 þ 0.01 4638 4.00 6.6 1.320 61 þ 30 4.2 þ 0.4s 400 141.15 510 0.703 72007 7.92 11.1 1.582 71 þ 24 4.2 þ 0.4

Nakhla C,02,457 mg

250 0.12 258 þ 22 5.00 þ 0.15 31 0.12 0.177 1.0089 68 þ 8 3.2 þ 0.5300 0.14 270 þ 25 5.20 þ 0.12 38 0.14 0.231 1.0638 61 þ 8 3.6 þ 0.5400 0.14 265 þ 25 5.10 þ 0.12 37 0.14 0.238 1.0518 59 þ 7 3.9 þ 0.6500 0.12 468 þ 22 5.00 þ 0.15 56 0.12 0.252 1.0589 48 þ 6 4.1 þ 0.6600 0.29 5200 þ 54 1.66 þ 0.04 1508 0.21 0.252 1.3540 82 þ 9 4.2 þ 0.6800 3.63 12600 þ 131 1.02 þ 0.03 45738 1.48 1.770 2.4100 84 þ 12 3.9 þ 0.4

1000 2.33 5907 þ 62 1.11 þ 0.03 13763 1.10 1.402 2.3600 78 þ 12 4.5 þ 0.41200 30.55 320 þ 8 0.75 þ 0.02 9776 3.88 4.445 1.7420 87 þ 13 4.4 þ 0.41550 96.92 45 þ 3 0.69 þ 0.01 4361 3.34 3.882 1.3600 86 þ 24 4.6 þ 0.4

Total 134.24 561 0.72 75309 10.53 12.649 1.7296 83 þ 16 4.4 þ 0.4

Nakhla C,11,59 mg

9 500 0.09 270 þ 50 5.10 þ 0.25 24 ^ 0.1 1.01 ^ 3.5 þ 0.69 1000 6.40 11400 þ 140 0.79 þ 0.02 72960 1.16 1.6 1.82 72 þ 12 3.8 þ 0.5

1550 139.61 96 þ 3 0.71 þ 0.02 13403 9.36 9.7 1.39 97 þ 26 4.0 þ 0.5s 500 146.01 591.5 0.713 86363 10.51 11.3 1.45 93 þ 24 4.0 þ 0.5

The data are corrected for system blanks and instrumental mass discrimination.The 36Ar, 40Ar, and 36Art abundances are in units 10310 cm3 STP/g and the 132Xe abundances are in 10312 cm3 STP/g.

EPSL 6189 26-4-02


5. Nakhla nitrogen: an exercise in multi-component resolution using two isotopes

The measured N abundances and isotopic com-positions are listed in Table 3. Nitrogen abundan-ces in all Nakhla samples are comparable and soare the bulk N

15N signatures in these samples. Nreleased in the 9 300‡C temperature steps indi-cates not only terrestrial contamination but pos-sibly also a minor indigenous light N component(N15N =330x) of the type present in Chassignyand ALH84001 [12,33]. These data are consistentwith the results of Wright et al. [34] who carriedout a stepped combustion study of Nakhla. Theyreported a range of N15N =310 to +13x in com-bustion steps of Nakhla consistent with the light-est N signature seen in our samples and also withthe 300^550‡C steps. The N released in the tem-

perature range 300^550‡C (s 70% of the nitrogenin Nakhla C,02) as well as N in the 1000‡C stepshows a uniform component of N

15NW+13x(Fig. 5). On the other hand, the 600^900‡C stepsshow systematically heavier N, with N

15N = 30^40x. This is the temperature range in whichthe previously discussed modern Martian atmo-spheric Xe component is observed. It seems likelythat also Martian atmospheric nitrogen may havebeen added. We may estimate a Martian atmo-spheric component, using a ratio 14N/40Ar = 3.0for the Martian atmosphere [6,35], coupled to aratio 40Ar/132Xe = 1.7U106 (based on atmosphericratios 40Ar/36Ar and 36Ar/132Xe of 1900 and 900,respectively [31,32]), and we obtain a ratio 14N/132Xe = 5.1U106. The estimated atmospheric Ncomponent amounts to 0.0203 ppm or 13% ofthe N in the 600^1000‡C temperature fractions.

Table 3Nitrogen abundances and isotopic composition in Nakhla

Sample T N N15N Sample T N N

15N(‡C) (ppm) (x) (‡C) (ppm) (x)

Nakhla C,02, 457 mg 120 0.020 0.6 þ 1.6 Nakhla C,01, 112 mg 120 0.020 0.8 þ 2.4200 0.040 34.5 þ 0.6 250 0.396 35.1 þ 0.6250 0.051 33.7 þ 0.6 300 0.157 34.1 þ 0.6300 0.592 9.8 þ 0.8 400 0.281 1.7 þ 0.8350 0.129 9.2 þ 1.6 400C 0.088 13.0 þ 1.3400 0.143 9.6 þ 1.4 600 0.033 36.0 þ 1.0450 0.144 9.3 þ 1.6 700 0.030 39.9 þ 1.9500 0.117 10.3 þ 1.0 700C 0.093 15.5 þ 1.2450C 0.108 14.6 þ 1.5 850 0.170 35.9 þ 1.5550 0.081 13.1 þ 1.6 1000 0.039 29.3 þ 1.1600 0.034 31.4 þ 1.8 1200 0.617 64.7 þ 2.2700 0.049 34.1 þ 2.0 1550 0.030 61.6 þ 4.3800 0.039 40.0 þ 3.3 Totala 1.934 26.8 þ 1.4900 0.022 39.1 þ 1.71000 0.008 12.0 þ 2.11200 0.019 276.4 þ 4.0 Nakhla C,11, 59 mg 120 0.024 0.9 þ 1.81400 0.071 278.6 þ 3.6 200 0.017 34.1 þ 2.31550 0.027 142.2 þ 2.8 250 0.028 36.2 þ 1.71600 0.002 163.7 þ 12.8 350 0.653 11.9 þ 1.1

Totala 1.676 28.4 þ 1.4 500 0.462 15.2 þ 1.5450C 0.271 13.8 þ 1.4700 0.205 21.7 þ 1.5900 0.048 39.5 þ 1.41000 0.040 42.4 þ 2.51550 0.568 70.1 þ 3.11600 0.020 35.2 þ 5.8

Totala 2.311 28.9 þ 1.8

C denotes a combustion step in 5 Torr O2. There are more temperature extractions for nitrogen than for Ar and Xe since thelatter gases from several extractions were combined to improve their measurement statistics.a These do not include the 120‡C extraction that released N consistent with terrestrial atmosphere.

EPSL 6189 26-4-02


In fact, a 13% atmospheric N component withN

15N = 620x [36] added to (87%) interior N(N15N =V13x [12]) predicts for Nakhla 600^1000‡C steps N

15N values of V100x, but onlyN

15N =V50x if either the measured N15N of

300x [6^8] in shergottite glasses is used for Mar-tian atmospheric N, or if a factor of two fraction-ation (favoring 132Xe) in the 14N/132Xe ratio isassumed in the process of incorporation. Wealso consider a possible, but unlikely alternativesource for heavy nitrogen, a cosmogenic 15Nc

component in the 6 1000‡C steps.An inspection of Fig. 5 shows that the

s 1000‡C data show N15N data up to 280x,

which are due to the spallation 15Nc componentproduced during the 11 Ma cosmic-ray exposureage. Using a 4Z-production rate [37] and atrapped signature N

15N = 13x, we predict a15Nc excess of 0.128 ng/g, which may be com-pared to the measured 15N excesses of0.130 þ 0.005 ng/g, for the s 1000‡C steps in the

three Nakhla samples. Therefore, the observedspallation 15Nc component in steps above1000‡C is not only expected, but it also accountsfor the entire spallation budget. Therefore, any15NC in the 6 1000‡C data is at best only a minorcomponent. This conclusion is supported by theArC spallation data in the 6 1000‡C temperaturesteps, which indicate a spallation componentof 6 3%.

An interesting trend in the nitrogen signature ofALH84001 was seen in a correlation N

15N vs. the129Xe/132Xe ratios [11] and suggested that Martianatmospheric N had an evolved signature ofN

15N = 7x about 4 Ga ago. Fig. 6 shows a mix-ing line for N

15N Nakhla data. The high 129Xe/132Xe end member represents the Xe reservoir‘modern Atm’ which includes an N componentwith N

15N =V40x, and the low 129Xe/132Xemember (close to Chass-E) apparently represents

Fig. 6. A trend line, apparently due to two-component mix-ing, is shown between the N

15N and 129Xe/132Xe ratios inNakhla. Note that fewer N fractions are shown, because Xefrom several steps was analyzed together, and the nitrogenisotopic compositions represent the summed data. For com-parison, the early atmospheric composition inferred fromALH84001 is indicated [11,12].

Fig. 5. The stepwise nitrogen release is shown for NakhlaC,02. Note the break in the ordinate. The 600^900‡C stepsrelease N which is isotopically heavier than the N released inlower temperature steps. The shifts to heavy N in thes 1000‡C steps are due to the spallation nitrogen component.The numbers assigned to data bars indicate the extractiontemperature in 100‡C.

EPSL 6189 26-4-02


interior N data, similar to data observed in Chas-signy [12]. In summary, Fig. 6 shows that an an-cient atmospheric component of the type presentin ALH84001 is not a viable end member of the Ncomponents in Nakhla.

6. Chronology and origin of Martian volatiles

The observed isotopic and elemental signaturesin interior components should help to constrainthe origin of Martian volatiles. We ¢rst assess theXe components.

As discussed, the ¢ssion Xe in Nakhla is due tothe decay of extinct 244Pu in the early history ofMars. The ¢ssion gas was not lost during theevolutionary processes on Mars which also af-fected the interior, including the event 1.3 Gaago, which did reset the radiometric clocks. The¢ssion component was assimilated and well mixedwith interior xenon with an initial signature ofChass-S.

The observed radiogenic excess of 182W(OWV3) and the sub-chondritic ratios 180Hf/184Win Nakhla (Lee and Halliday [38]) imply a historyof Hf/W fractionation that relates to the accre-tionary time of Mars. These authors suggest anage di¡erence in the time of accretion of Mars,relative to that of the solar system, of V5 Ma,using a model of concomitant accretion and coreformation. The evidence for early formation anddi¡erentiation of Mars is supported by Sm^Nddata which show a radiogenic excess of 142Nd inNakhla [39], and by the interior trapped Xe com-ponent with ¢ssion Xe from extinct 244Pu. Positiveexcesses in radiogenic 142Ndr indicate roughly si-multaneous enrichment in Hf/W and Sm/Nd ra-tios and early development of mantle sources inMars with Sm/Nd ratios which exceeded thechondritic value and which di¡ered from the com-position observed in Nakhla today.

An evolutionary parameter available from theXe isotopic abundances is the ratio of radiogenic129Xer to ¢ssion 136Xef in Martian reservoirs. Thisratio was rapidly evolving in the earliest stages ofMartian evolution due to the di¡erences in half-lives of the nuclides 129I (T1=2 = 16 Ma) and 244Pu(T1=2 = 82 Ma). The ratio 129Xer/136XefW6 ob-

served in Nakhla (s 1000‡C steps) is similar toratios reported in ALH84001 [12], but is lowerby more than an order of magnitude than theratio in the modern Martian atmospheric compo-nent, as observed in shergottites [22,28].

We may consider elemental ratios 36Ar/132Xeand 84Kr/132Xe vs. the ratio 129Xe/132Xe (Fig. 7)in bulk samples. Nakhla data plot close to trendlines observed in ALH84001 data, except for theatmospheric component (800‡C and 1000‡C data).The measured Lafayette iddingsite data [15,18]also plots on this trend line in the lower panel(no 36Ar/132Xe ratio was published). This trendline misses the modern Martian atmospheric da-tum (indicated by arrows in Fig. 7). In this plot

Fig. 7. The elemental ratios 36Ar/132Xe and 84Kr/132Xe corre-late with the ratios 129Xe/132Xe in Nakhla. In the lower panelthe iddingsite data from Lafayette [15,18] is also shown (un-certainties in the Lafayette data [15,18] are larger than thoseshown for our Nakhla samples). The ‘early atmospheric’component observed in ALH84001 [12] is indicated, as wellas the (o¡-scale) ratios in modern Martian and terrestrial at-mospheres (arrows). Chass-S and Chass-E data and referen-ces to ALH84001 data are from [12].

EPSL 6189 26-4-02


the end-member composition with high 129Xe/132Xe ratio is compatible with the ancient atmo-spheric component observed in ALH84001 [12],while the low 129Xe/132Xe end-member ratios arenot consistent with either the Chass-S or theChass-E signatures. These end-member elementalratios suggest either Ar/Kr/Xe elemental di¡eren-ces, or large fractionations relative to signaturesin the modern Martian atmosphere. It is alsogood to keep in mind that the Xe isotopic signa-tures for interior components are of solar type,while atmospheric Xe is fractionated by 37xper mass unit [22]. We further note that the36Ar/132Xe and 84Kr/132Xe ratios in the inferredatmospheric component (800‡C and 1000‡C steps)do not plot close to ‘modern Martian atmosphere’indicating that the atmospheric component inNakhla was elementally fractionated [9,15,17,18].

Noble gas data in Nakhla have been interpreted[15,18] as an outcome of Martian weathering pro-cess (formation of clay minerals by aqueous alter-ation on Mars), whereas the ALH84001 data mayrepresent the early planetary atmosphere [10,12].The trapped 36Ar abundances in Nakhla andALH84001 are comparable (V1U1039 cm3

STP/g), but the radiogenic 129Xer component inNakhla is lower by a factor of V5.

We note that the 129Xe/132Xe and 40Ar/36Ar ra-tios in the modern Martian atmospheric compo-nent have been extensively used in models of theoutgassing history of the planet [40^42], beforeinformation about the Martian interior compo-nents was available. Potentially informative evolu-tionary parameters like the ratio of two radiogen-ic nuclides, 40Ar and 129Xer are still missing. Inthis case, 40Ar represents the atmospheric 40Arabundances and 129Xer represents the 129Xe ex-cesses relative to Chass-S (the interior compo-nent). In such cases where measured 40Ar abun-dances can be corrected for in situ producedradiogenic components, the inferred ratios maythen be related to a modern atmospheric ratioof 1.4U106 [22]. In ALH84001 the ‘ancient atmo-spheric’ 40Ar/36Ar ratio of 6 150 and the mea-sured radiogenic 129Xer [12] yield a ratio 40Ar/129Xer 6 3U104.

The data from ALH84001 suggested that ex-changes with the atmosphere occurred at a time

when the atmospheric 129Xe/132Xe ratio hadevolved to a value of 2.16, but that the other Xeisotopes had retained solar-type (Chass-S) Xe iso-topic composition [12]. Gilmour et al. [10] in-ferred an approximate time of 4.0 Ga for the Xeincorporation into orthopyroxene. The time whenNakhla exchanged volatiles with the atmospherecan only be constrained by the presence of anunmixed modern atmospheric Xe component inthe low-temperature (600^1000‡C) fractions,which imply a recent system opening (9 1.3 Gaago), possibly as late as the ejection event onMars.

7. Conclusions

Nitrogen, argon, and xenon isotopic abundan-ces have been determined in a stepwise release ofgases from the Nakhla meteorite. The observedisotopic signatures identify unmixed ancient andmodern Martian atmospheric components. Themass-fractionated modern Martian atmosphericXe component is released early at temperaturesof 600^1000‡C, and indicates a recent incorpora-tion into Nakhla. The inferred Martian interiorXe component is consistent with an evolvedChass-S Xe component which assimilated a ¢ssioncomponent in the Martian interior. The isotopicsignatures of N also show that ancient and mod-ern components in Nakhla were not mixed. The¢ssion Xe abundances in the evolved trappedNakhla component exceed those derived from insitu decay of 238U in 1.3 Ga by a factor of 16, andthe Xe signature identi¢es extinct 244Pu as theprogenitor which did not decay in situ. The ob-served elemental ratios 36Ar/132Xe and 84Kr/132Xein Nakhla are similar to those in ALH84001.

Acknowledgements

We thank the British Natural History Museumfor the Nakhla sample and G. Kurat for his helpin mineral characterization. Detailed commentsby U. Ott and suggestions by two anonymousreviewers improved the manuscript. Work sup-ported by NASA Grant NAG5-8167.[AH]

EPSL 6189 26-4-02


Appendix 1

Measured Xe isotopic ratios in Nakhla. The 132Xe concentrations are in units 10312 cm3 STP/g.

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[15] M.J. Drake, T.D. Swindle, T. Owen, D.S. Musselwhite,

Sample T 132Xe 124Xe/132Xe 126Xe/132Xe 128Xe/132Xe 129Xe/132Xe 130Xe/132Xe 131Xe/132Xe 134Xe/132Xe 136Xe/132Xe(‡C)

Nakhla C,01,112 mg

400 0.11000 2.553 0.0433 þ 13 0.0696 þ 13 0.1664 þ 21 2.224 þ 35 0.2095 þ 20 0.9268 þ 106 0.3900 þ 32 0.3263 þ 291200 2.289 0.0583 þ 14 0.0951 þ 15 0.2039 þ 23 1.633 þ 33 0.2291 þ 19 0.9773 þ 111 0.4021 þ 33 0.3286 þ 301550 6.861 0.0287 þ 10 0.0458 þ 11 0.1367 þ 18 1.333 þ 27 0.1873 þ 17 0.8697 þ 95 0.4105 þ 29 0.3508 þ 26

Totala 11.703 0.0377 þ 12 0.0607 þ 13 0.1563 þ 20 1.586 þ 30 0.2003 þ 19 0.9032 þ 101 0.4044 þ 31 0.3411 þ 28

Nakhla C,02,457 mg

250 0.177 0.0030 þ 6 0.0031 þ 6 0.0705 þ 15 1.009 þ 9 0.1528 þ 25 0.7876 þ 80 0.3860 þ 40 0.3301 þ 35300 0.231 0.0040 þ 8 0.0035 þ 8 0.0715 þ 11 1.064 þ 8 0.1521 þ 16 0.8011 þ 100 0.3854 þ 55 0.3290 þ 42400 0.238 0.0042 þ 5 0.0043 þ 5 0.0835 þ 15 1.052 þ 9 0.1591 þ 17 0.7813 þ 100 0.3792 þ 52 0.3172 þ 42500 0.252 0.0038 þ 6 0.0043 þ 6 0.0831 þ 15 1.059 þ 8 0.1617 þ 19 0.7822 þ 100 0.3817 þ 49 0.3184 þ 40600 0.252 0.0036 þ 6 0.0043 þ 6 0.0789 þ 14 1.354 þ 9 0.1609 þ 19 0.7822 þ 100 0.3819 þ 55 0.3230 þ 45800 1.832 0.0259 þ 6 0.0409 þ 7 0.1248 þ 14 2.384 þ 18 0.1847 þ 15 0.8679 þ 62 0.3928 þ 27 0.3380 þ 21

1000 1.484 0.0400 þ 7 0.0641 þ 8 0.1577 þ 17 2.322 þ 23 0.2042 þ 17 0.9117 þ 66 0.3910 þ 29 0.3294 þ 241200 4.625 0.0293 þ 9 0.0469 þ 10 0.1381 þ 18 1.739 þ 12 0.1886 þ 17 0.8763 þ 64 0.4090 þ 24 0.3444 þ 221550 4.131 0.0435 þ 10 0.0704 þ 11 0.1713 þ 21 1.379 þ 12 0.2072 þ 17 0.9200 þ 64 0.4100 þ 28 0.3400 þ 23

Total 13.22 0.0322 þ 8 0.0516 þ 9 0.1436 þ 18 1.727 þ 14 0.1929 þ 17 0.8850 þ 67 0.4027 þ 29 0.3386 þ 24

Nakhla C,11,59 mg

500 0.11000 1.771 0.0676 þ 15 0.1102 þ 17 0.2218 þ 36 1.805 þ 36 0.2444 þ 32 1.0152 þ 124 0.3849 þ 48 0.3095 þ 421550 10.123 0.0312 þ 16 0.0500 þ 19 0.1395 þ 39 1.402 þ 43 0.1913 þ 35 0.8833 þ 113 0.4056 þ 47 0.3453 þ 39

Totala 11.894 0.0366 þ 16 0.0589 þ 19 0.1517 þ 39 1.462 þ 42 0.1992 þ 35 0.9030 þ 115 0.4025 þ 47 0.3400 þ 39

Uncertainties listed are those in the least signi¢cant ¢gures of the isotopic ratios (2c).a Total 132Xe in Nakhla samples C,01 and C,11 do not include the lowest temperature release (6 1% of the total) that had iso-topic composition consistent with terrestrial atmospheric Xe.

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martian atmospheric and interior volatiles in the meteorite nakhla

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