Volatiles: Constraints on disk evolution, and

planetesimal/planets accretion

Conel M. O’D. Alexander

DTM, Carnegie Institution of Washington

Meteorites Recorders of first few million years (Ma)

4,567.3±0.2 million years old

Chondrites

1 cm

Irons

Achondrites

Formed in <2 Ma Formed in ~2-4 Ma

Allende (CV3)

Lancé (CO3)

Chondrites – ‘cosmic’ sediments

Photomicrographs Courtesy Adrian Brearley

Three basic components: Chondrules, CAIs, Matrix.

Enstatite – EH, EL Ordinary – H, L, LL (and R) Carbonaceous – CI, CM, CR, CV, CO, CK

~2 cm

~2 cm

Time constraints – Asteroids-Mars

1

2

3

4

0

Formation of CR chondrites

Tim

e a

fter

CV

CA

Is (

Ma)

Formation of O+R chondrites Formation of E chondrites

Formation of CK chondrites Formation of CV+CO chondrites

Formation of CI, CM+TL chondrites

Formation of angrite parent body

Vesta (HEDs)

Mars (~50%)

26Al no longer an effective heat source

Dissipation of the gas disk (and Grand Tack?)

ProtoJupiter = 20 Mearth

t0=4,567 Ma (Connelly et al. 2012)

Time constraints - Earth t0=4,567 Myr (Connelly et al. 2012)

10

20

30

40

0

Tim

e af

ter

CV

CA

Is (

Ma)

Retention of atmosphere (Avice and Marty 2014)

Formation of the Moon (Touboul et al. 2007; Barboni et al. 2017)

50

Dissipation of gas disk (and Grand Tack?)

Debris disk

Jupiter reaches 20 Mearth?

Time constraints - Earth

4,567 Ma (Connelly et al. 2012)

50

100

150

200

0

Evidence for oceans from oldest zircons (Wilde et al. 2001)

Tim

e af

ter

Sola

r Sy

stem

fo

rmat

ion

(M

a)

Retention of atmosphere (Avice and Marty, 2014)

Formation of the Moon (Touboul et al. 2007)

What did the Earth accrete and when was it

accreted?

-500

-300

-100

100

300

500

700

900

1100

-1000 -500 0 500 1000 1500

d15N

(‰

)

dD (‰)

TL

CI

Earth E

arth

CM

CR

Solar

JFC

OCC

Mars

(Comets – H from H2O, N from HCN/NH3)

Comets JFC – Jupiter Family OCC - Oort Cloud

Asteroids and Comets

Marty et al. (2016) – cometary contributions to H-C-N were minor, but may have been important for noble gases.

Venus

d(‰)=(R/Rstd-1)x1000 R=D/H or 15N/14N

Earth’s siderophile isotopes All inconsistent with carbonaceous chondrites

Eart

h

Eart

h

Earth

Of the carbonaceous chondrites, the CIs are closest to the Earth’s composition.

Nevertheless, if CI-like material was the source of the volatiles, it must have accreted before the end of core formation – assumed to be Moon-formation.

The late veneer after Moon-formation was too little and too dry.

Atmosphere ≠ interior

Mantle Ne – Solar or implanted solar wind (and H & He?)

Péron et al. (2017)

Either the atmosphere was not degassed from the interior, or the interior/atmosphere compositions have change after degassing?

‘Chondrite’

-500

-300

-100

100

300

500

700

900

1100

-1000 -500 0 500 1000 1500

d15N

(‰

)

dD (‰)

TL

CI

Earth E

arth

CM

CR

Solar

JFC

OCC

Vesta Mars

Angrite

Crystallization ages Angrite D’Orbigny ~3.5 Ma after CAIs HED Stannern ~3.6 Ma after CAIs

Accretion ages of CIs and CMs ~3.5 Ma after CAIs (Fujiya et al. 2013)

Did early planetesimals fully degas?

Venus

(Miura & Sugiura 1993; Abernethy et al. 2013; Sarafian et al. 2014,2017; Barrett et al. 2016)

Where did the carbonaceous chondrites

form?

Trouble with Saturn’s moons

ISM ices

Bulk solar

Earth

Enceladus H2O

Comets

Titan – CH4

Yang et al. (2013)

Chondritic H is a mix of H2O and organics

-500

-300

-100

100

300

500

700

900

0 2 4 6

Bulk

dD

(‰

)

Bulk C/H (wt.)

CI

Tagish Lake

CM

CR

-500

0

500

1000

1500

2000

2500

3000

3500

4000

0 5 10 15 20 25

dD

(‰

)

C/H (wt.)

Organics

CM water

CR water

(Alexander et al. 2012)

Chondritic water was not from the outer Solar System

After Alexander et al. (2012)

1.E-05

1.E-04

1.E-03D

/H R

atio

CO

Tagish

Lake

JFC

OC

RC

Protosolar

Earth

Enceladus

Oort Cloud comets

CR

CM

CI

4000

3000

2000

1000

0

-200

-400

-600

-800

dD

(‰)

?

3Fe + 4H2O = Fe3O4 + 4H2

(Alexander et al. 2010)

0

2000

4000

6000

8000

10000

12000

0.01 0.1 1

dD

(‰

) of

resi

dual

H2O

Fraction of H2O remaining

0°C

200°C

Rayleigh fractionation

1.0E-05

1.0E-04

1.0E-03

0.1 1 10 100

D/H

in

Wate

r

Distance (AU)

Earth

Enceladus

Comets

Chondrites

Titan

(CH4)

Solar

GT

Saturn

LL CR

CM CI

H isotopes: Indicators of formation distance?

JFC

s

OC

Cs

Summary • All chondrites accreted their volatiles in a ~CI-like matrix. C, N, noble

gases and some H was in a macromolecular organic matter. H2O was accreted as ice that also included CO2 and HCN/NH3. No chondrite seems to have accreted their full solar H2O complement.

• The initial D/H of water in CCs and non-CCs were not very different, contrary to model expectations, and less than Enceladus or even Titan.

• From these perspectives, there are no compelling reasons for the CCs to have formed in outer Solar System, or at least not beyond the location of Saturn when its moons formed (3-7 AU in the Grand Tack).

• CI/CM-like material was the major source of terrestrial planet H+N+C, perhaps with some solar input, but comets may have been much more important for noble gases.

• Atmospheric volatiles were accreted before Moon-formation and may not have been initially stored in the Earth’s interior, yet somehow they survived impacts large and small.

1.0E-04

1.0E-03

1.0E-02

1.0E-01

0 2 4 6 8 10 12 14

Bu

lk E

art

h/C

I

Cs

C

Pb Cl

H

N

36Ar Kr

Xe

Br I

Cd

10-3

10-4

10-2

10-1

Late Veneer

Ne

(Dereulle et al., 1992; Marty, 2012; Palme and O’Neill, 2014)

Gradual Xe loss (Pujol et al. 2011)?

Hidden reservoir or impact loss?

Roughly chondritic volatiles

2-4% CI/CM like material

N isotopes: Indicators of formation distance?

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.1 1 10 100

15N

/14N

Distance (AU)

Am

ino

Acid

s

Earth

Solar

Titan

Comet HCN/NH3

(averages)

Chondrites (bulks)

GT

Strecker-cyano synthesis R-C=O + HCN + NH3 + H2O = R-CNH2-COOH

Saturn

’Twin’ planets are not identical

Venus abundances just for atmosphere

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01

Ven

us/

CI

Earth/CI

Ne

Kr

N

C

36Ar

Xe

40Ar

Comets or Solar wind?

Volatiles in matrix

0.0

0.5

1.0

1.5

2.0

2.5

500 1000 1500 2000

Ab

un

dan

ce/C

I

50% Condensation Temperature (K)

Bulk CV chondrites

Lithophiles

Siderophiles

ChalcophilesMatrix

(Wasson and Kallemeyn, 1988)

Volatiles in matrix

0

50

100

150

200

250

300

350

0 20 40 60 80 100

Bu

lk Z

n (

pp

m)

Matrix (vol.%)

CM

CI

TL

CO,CV,CR OC

RC

(Wasson and Kallemeyn, 1988; Rubin and Wasson 1993: Brown et al. 2000)

Non-CC

CC

Volatiles in matrix

(Alexander et al. 2012,2014)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 20 40 60 80 100

Bu

lk C

(w

t.%

)

Matrix (vol.%)

CM

CI TL

CO,CV,CR

OC

Presolar grains in matrix (Xe-HL carried by supernova nanodiamonds)

(Huss and Lewis 1995; Huss et al. 2003)

0.0

0.5

1.0

1.5

2.0

2.5

0 20 40 60 80 100

Bu

lk 1

32X

e H

L (

10

-10 c

c/g)

Matrix (vol.%)

CM

CI

CV

CO,CR

OC

Volatiles in matrix

(Alexander et al. 2012)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 20 40 60 80 100

Bu

lk H

(w

t.%

)

Matrix (vol.%)

CI

CM

TL

CV

CO, CR

OC

Story so far • The abundances of highly volatile elements, organic C, presolar

circumstellar grains and water suggest that matrices in ALL chondrites are dominated by ~CI-like material.

• If correct, since the ECs, OCs & RCs all formed ~2 Ma after CAIs:

(1) CI-like material was present in the inner Solar System >2 Ma before a possible Grand Tack, and ~1 Ma after the inner Solar System was possibly sealed off by a growing Jupiter.

(2) The snowline was already in the inner Solar System by 2 Ma. The main building blocks of the terrestrial planets may not have been initially volatile-free, but if formed <3-3.5 Ma after CAIs they were heavily modified by internal heating due to 26Al.

D/H in H2O: an indicator of formation distance from the Sun?

Comets

Horner et al. (2007)

(D/H

) H2

O/(

D/H

) H2

Distance from the Sun (AU)

Interstellar H2O

Solar

Earth

Enceladus

High T H2O

Turbulent mixing

Rosetta results

<10% to >90% of terrestrial 36Ar may be cometary (Marty et al. 2016)

22±5% of Xe from comets (Marty et al. 2017)

-500

-300

-100

100

300

500

700

900

1100

-1000 -500 0 500 1000 1500

d15N

(‰

)

dD (‰)

Earth E

arth

Solar

Mars

Jaupart et al. (2017) – Ne, at least, in embryos not from primordial atmospheres.

Not primordial atmospheres

Venus

d(‰)=(R/Rstd-1)x1000 R=D/H or 15N/14N

Corrected water H isotopes

1.E-05

1.E-04

1.E-03W

ater

D/H

Rat

io JFC

LL

RC

Protosolar

Earth

Enceladus

Oort Cloud comets

CR

CM CI

4000 3000

2000

1000

0 -200

-400

-600

-800

dD

(‰)

10-3

10-4

10-5

(Sutton et al. 2017)

1.0E-05

1.0E-04

1.0E-03

0.1 1 10 100

D/H

in

Wate

r

Distance (AU)

Earth

Enceladus

Comets

Chondrites

Titan

(CH4)

Solar

GT

Saturn

H isotopes: Indicators of formation distance?

JFC

s

OC

Cs

A possible alternative?

• There was a burst of early planetesimal formation involving material that had been thermally processed by FU Orionis outbursts and from which CAI material was extracted.

• By 2 Ma this material was nearly exhausted and material from the outer Solar System (matrix) began diffusing in and dominated later formed planetesimals. This material included refractory inclusions (CAIs and AOAs).

Accretion times and water contents

0

0.5

1

1.5

2

2.5

3

3.5

1 1.5 2 2.5 3 3.5 4

Accretion time (Ma) after CAIs

E

O,R CV

CR

CI

CO

CK

CM

?

Accretion times modified after Sugiura and Fujiya (2014)

Clearing of inner disk? Grand Tack?

Now Dry

Differentiated Lithified

Wet

Damp

Dry

Wat

er c

on

ten

t o

n a

ccre

tio

n

Summary

Accretion ages: Sugiura and Fujiya (2014) Chondrule ages: OC Al-Mg, Kita et al. 2008, Villeneuve et al. 2009; OC Hf-W, Kleine et al. 2008; CO Al-Mg, Kurahashi et al. 2008; CV Al-Mg (Kaba) Nagashima et al. 2015; CV Hf-W Budde et al. 2016; CR Al-Mg Schrader et al. 2017.

0

1

2

3

4

0 1 2 3 4

Mean

ch

on

dru

le a

ge a

fter

CA

I (M

a)

Accretion age after CAI (Ma)

OC 26Al

OC 182Hf

CO

CV 26Al

CV 182Hf

CR

CR

CV

CO OC

Volatiles from primitive meteorites

Marty et al. (2012, 2013)

Asteroidal Sources Bus and Binzel (2002)

Warren (2011)

Hsieh and Jewitt (2006)

Hu

nga

ria≈

EC

S-complex≈OC+RC

C-complex≈CC

Altwegg et al. (2015)

D/H in Solar System objects

Comets

Volatiles from primitive meteorites

Marty et al. (2013)

help

Time constraints

4,567 Myr (Connelly et al. 2012)

50

100

150

200

0

Evidence for oceans from oldest zircons (Wilde et al. 2001)

Tim

e a

fter

So

lar

Syst

em f

orm

atio

n (

Myr

)

Retention of atmosphere (Avice and Marty, 2014)

Formation of the Moon (Touboul et al. 2007)

-500

-300

-100

100

300

500

700

900

1100

-1000 -500 0 500 1000 1500

d15N

(‰

)

dD (‰)

TL

CI

Earth

Ear

th

CM

CR

Solar

JFC

OCC

Vesta Mars

Moon

Angrite

(Comets – H from H2O, N from HCN/NH3)

Comets JFC – Jupiter Family OCC - Oort Cloud

What’s the issue?

• There was CI/CM-like material in the inner Solar System well before there could have been a Grand Tack (>4 Ma), but after Jupiter may have sealed off the inner Solar System (≤1 Ma).

• Minor irritant or big problem? Depends on how much and how much earlier.