volatiles: constraints on disk evolution, and planetesimal ... constraints on disk evolution, and...
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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.