Isotope abundance anomalies
in meteorites: CAIs and
presolar grains
U.Ott
Rußbach
March 16, 2010
Rough outline:
 introduction
 recognition of isotope anomalies
 anomalies in high-temperature
inclusions (Ca-Al-rich, CAIs)
 presolar grains
Meteorites - Messengers from Space
Murchison (carbonaceous chondrite)
Ochansk,
Russia (Heide)
micrometeorite
ALH 81032 (ordinary chondrite)
Earth: accretes ~ 40,000 tons of extraterrestrial material
each year – some of it can be recovered as meteorites
parent bodies of meteorites
= mostly asteroids from the main belt as indicated by, e.g., the orbital
characteristics of those for which a trajectory could be determined
also more recently:
Neuschwanstein,
Puerto Lapice (Vesta)
Almahata Sitta
Schultz
in addition some from the Moon, from Mars, from comets (?)

isotopic anomalies
= isotope abundance anomalies
(short form)
 observed as isotopic variations in
“primitive“ matter
 meteorites
 which, however, are also the best
reference for mean composition of
the Solar System
(and not only of deviations thereof)
 meteorites are important for astrophysics
 “historic“
abundance curve
(Suess and
Urey, 1956; as in
Fowler, 1984);
largely based
on meteorites
 overall and fine
structures
 the processes
 good “solar“ data
 good input for
nucleosynthesis
and GCE models
however:
 Solar System
composition
= result of
mixture from
many nucleosynthetic
sources /
processes
 anomalies allow
to track
individual
contributions
identifying anomalies - technical:
 technique: mass spectrometry,
after appropriate handling / preparation / isolation
of samples
 mass spectrometric technique depending on problem:
thermal ionization mass spectrometry (TIMS),
inductively coupled plasma (ICP-MS), gas mass
spectrometry, secondary ion mass spectrometry
(SIMS), resonance ionization (RIMS)
 most sensitive to “foreign“ additions: noble gases
(because of their low abundance in rocks)
 have played special role in the detection of
presolar grains in meteorites
identifying anomalies - pitfalls:
 need to distinguish nucleosynthetic contributions
(true anomalies) from “trivial ones“
 i.e. variations caused by processes acting in the
Solar System (still today)
 like
-- radioactive decay of long-lived nuclides, e.g.
U, Th4He, Pb isotopes, 40K  40Ar, 40Ca,
87Rb87Sr
-- spallation reactions caused by cosmic ray
irradiation
-- mass dependent fractionation during physicochemical processes
how to distinguish:
 radiogenic contributions:
mostly mono-isotopic, correlate with parent
 cosmogenic:
typical spectrum ~ equal abundance of isotopes
 mass dependent fractionation:
more tricky to rule out
 for some two-isotope elements (C, N, e.g.):
only definitely ruled out if effects unreasonably
large (such as in presolar grains);
other cases (e.g. U, Tl)  Maria Schönbächler
fra
 if more than
two isotopes:
deviations from
scaling with
mass difference
CA
io
t
a
on
i
t
c
n
Is
R.N. Clayton
TF = terrestrial fractionation line:  17O = 0.52 x  18O
where  iO = deviation (‰) of iO/16O from SMOW
(standard mean ocean water)
McCulloch
 where mass differences
are large (e.g. Ca) and
mass fractionation large
 fractionation law
= critical choice
 here: differences up to 5
‰ in corrected ratios
depending on law – vs.
precision, often 0.01 ‰
CAI anomalies
Ca-Al-rich inclusions CAIs = high temperature condensates
probably first solid materials formed within Solar System
 original idea:
supernova 16O
 now: non-nuclear (?)
 CAI line = slope 1 =
admixture of pure 16O (?)
– up to ~4%
 think self-shielding
think stratosphere
 ~ mm size:
- chondrules
- CAIs
 ~ µm or less:
presolar grains
 CV3 meteorite Axtell (Meteoritics cover)
 but others are clearly of nuclear origin, e.g.
26Mg excesses from decay of 26Al (T = 0.7 Ma)
½
(more about extinct radionuclides in ESS  Maria)
slope
canonical
ESS value
initial
Lee
 most prominent anomalies in CAIs (except for O):
overabundances of neutron-rich isotopes of Fe peak
 “typical
CAI”
pattern
 effects
measured
in -units
(parts in
10,000)
Lugmair
 more evident:
in subclass of
FUN inclusions;
outstanding:
C-1, EK1-4-1;
combined with
strong massdependent
effects
(O, Mg, Si)
 note different
patterns
 C1: effects are
deficits
 EK-1-4-1:
note size  3%
Lugmair
astrophysical models: MZM vs. Kratz
“normal“CAIs
o.k.
 popular: multi-zone
mixing model (MZM)
of Hartmann, Woosley
and El Eid (1985) –
n-rich NSE
 K.-L. Kratz: charged
particle reactions +
subsequent r-process
Fe
EK1-4-1
Ca
Ti
Cr
Zn
 note:
 different patterns in FUN inclusions EK1-4-1
(positive) and C1 (negative)
 different patterns of the positive patterns in EK1-4-1
vs. non-FUN CAIs
 much larger (up to almost 30%) anomalies in hibonite
grains from CAIs, again different pattern
 large neutron-rich 54Cr-only enhancements (up to 2 %)
observed in stepwise dissolution of the most primitive
carbonaceous chondrites; small variations among
meteorite classes
 hibonites: up to 30 %
in 50Ti, 10 % in 48Ca
Ireland
 unfortunately only little data on rare (0.004%) 46Ca
Niederer 1984
(3.3 /13.9)
FUN inclusions only: heavy (p-, s-, r-) elements
 situation
simpler, but
only “in principle”;
few data only
p
 confusing in a way
p+r
 r-enhancements
(Sm, Nd, Ba) EK14-1 compatible with
“average r-process”
p
only p
 non-FUN:
even less data

(n-rich) with
50Ti correlated(?)
r
96Zr
McCulloch
FUN inclusions C1 and EK1-4-1
r
no p, but r
excesses: rratios ~ average
r
r
(or radiogenic deficit)
Barium, Strontium
p
p
deficits
McCulloch
Ca-Al-rich FUN inclusion EK1-4-1:
r-process overabundances in Nd
overabundance (%)
%
0.4
0.2
mass number
0.0
142 143 144 145 146 147 148 149 150
s
r,s
s,r
r,s
s,r
r,(s)
r
however: because of small effects assumptions in normalization
(mass-dependent effects) involved – unlike stardust
Presolar grain anomalies - stardust
vs. CAIs = formed within Solar System
 CAIs
contain some
material not
completely
homogenized
isotopically with
rest of Solar
System; but
formed within
 presolar grains
= stardust;
record earlier
stage; effects much
larger
0.4
overabundance (%)
0.2
Ca-Al-rich FUN inclusion EK1-4-1
0.0
0
deficit (%)
-20
-40
-60
presolar silicon carbide
s
r,s
s,r
r,s
s,r
r,(s)
r
142 143 144 145 146 147 148 149 150
mass number
-80
size + abundance matter
 CV3 meteorite Axtell (Meteoritics cover)
 ~ µm or less:
presolar grains
 ~ mm size:
- chondrules
- CAIs
(Ca-Al-rich)
first
condensates
 key to identification of presolar matter in meteorites:
 natural low abundance of noble gases in solids;
unusual isotopic structures of noble gases in presolar
materials can “shine through“ even in bulk analyses
Overview
mineral
diamond
silicon
carbide
30 ppm
graphite
1 ppm
corundum/
spinel
2 ppm
silicates
silicon
nitride
isotopic signatures
stellar source
contribution
Kr-H, Xe-HL, Te-H
supernovae
?
enhanced 13C, 14N, 22Ne, s-process elements
low 12C/13C, often enhanced 15N
enhanced 12C, 15N, 28Si; extinct 26Al, 44Ti
low 12C/13C, low 14N/15N
AGB stars
J-type C stars (?)
Supernovae
novae
> 90 %
<5%
1%
0.1 %
1500 ppm
enhanced 12C, 15N, 28Si; extinct 26Al, 41Ca, 44Ti
SN (WR?)
Kr-S
AGB stars
low 12C/13C
J-type C stars (?)
low 12C/13C; Ne-E(L)
novae
80 %
< 10 %
< 10 %
2%
enhanced 17O, moderately depleted 18O
enhanced 17O, strongly depleted 18O
enhanced 16O
> 200 ppm similar to oxides above
RGB and AGB
AGB stars
supernovae
> 70 %
20 %
1%
supernovae
100 %
enhanced 12C, 15N, 28Si; extinct 26Al
0.002 ppm
silicon carbide (left) and
graphite (right);
typically µm-sized
 single grain analyses by
ion microprobe,
~ 30 ppm in primitive
meteorites
co
nc
en
at
tr
hibonite: rare
e
nanodiamond (TEM): ~ 1000 C
atoms; abundant (~ 1.5 per mill)
on
Most clear-cut case: silicon carbide
 best (?) understood nucleosynthesis process:
s-process
Xenon in SiC vs. solar Xe
250
overabundance [%]
200
 takes place in He
shell of TP-AGB
stars
150
 most (>90%) of
presolar SiC
grains come from
AGB stars
50
s
s
100
s,(r)
r
0
p
r,(s)
p
-50
124
126
128
130
r,(s)
132
mass number
r
134
136
supported by
 distribution of C
isotope ratios similar
to distribution of
values determined
for atmospheres of
carbon stars
 condensation from
winds of C stars
 expected small
variations in Si
isotopes, expected
level of 26Al
( expected 26Mg
excesses)
Alexander et al., 1993
 groups in
plane N
isotopic vs.
C isotopic
compositions
 groupings
apart from
the ~90%
mainstream
grains
 for group
definition in
some cases
also Si
isotopes
needed
Ho
ppe
gray =
mainstream
slope
=1.35
schematic
mainstream
grains
mainstream-AGB
400
Meteoritic SiC
slope 1.34
line
200
 29Si/28Si (‰)
mostly due to GCE
0
-200
Hoppe
-400
-600
-800
~ 1% from SN
-1000
-800
-600
-400

Murchison Mainstr.
& type A, B, Y, Z
Murchison type X
Orgueil
-200
0
30Si/28Si
200
(‰)
400
600
 4 groups (carbon
isotopic clusters)
Hoppe
 a large fraction of
graphites from SN
 similar to these and SiC
type X grains: silicon nitride
 group 1 similar to
SiC-A and –B;
group 2 similar to
SiC mainstream;
group 3 normal C
isotopes (?)
group 4 similar to
SiC-X
 variety of stellar
sources indicated:
SN, novae, C stars
 SN grains: also extinct
44Ti (60a) and 49V (1 a)
 the case of the
oxide + silicate
grains: 4 groups
 essentially all
from Red Giants
 show evidence for
processes of
nucleosynthesis
occurring there
(e.g., dredged up
material from Hburning, HBB, CBP)
 also GCE effects
 similar: other
oxides / silicates
Nittler
[o /o o ]
Back to SiC and s-process:
100
most straightforward inferences
 e.g. Nd: the
importance of
nuclear data
Nd)
144
Nd/
-2 0 0
normal
-3 0 0
new

143
o ld  's
-1 0 0
-4 0 0
s-process
 1 5 0 N d /1 4 4 N d )
-5 0 0
[o /o o ]
700
o ld  's
146
Nd/
144
Nd)
600

 macroscopic
observations
(on aggregates),
and “classical
interpretation”:
observed
= mixtures of
“the s-process“
and “normal“
material
(from stellar
envelope);
0
500
400
300
new
200
100
0
-1 0 0 0
s-process
-8 0 0
-6 0 0
-4 0 0
-2 0 0
0
200
 1 5 0 N d /1 4 4 N d )
solar 138Ba/136Ba = 9.129
because of small n capture cross section,
138Ba abundance sensitive to n exposure
 analyses on grain size fractions of SiC (Prombo et al.):
neutron exposure sensitive ratio 138Ba/136Ba variable
 and implies some effective 0 (scaled to 30 keV) that
is only about half that needed to describe solar
system abundance distribution (~0.15 vs. ~0.30 mb-1)
 apart from neutron dose (exposure) – also neutron density
shows up in isotopic ratios; in cases of effective competition
between neutron capture and -decay (branchings)
 e.g. 134Cs branching

other important branchings, where information is contained
in isotopic signatures from presolar SiC:
Kr isotopes (79Se, 85Kr branchings), Sr isotopes (85Kr), Zr
isotopes (95Zr), Nd (147Nd), Sm (151Sm), Dy (163Dy);
plus some more subtle ones
normalized to Arlandini et al.
10
1
m
144
E/
Nd
Ba
Hf
Dy
0.1
Sm
Eu
Sm,Eu,Yb: upper limits
0.01
Er
Gd
Nd
140
150
mass
Yb
160
170
180
overall relative elemental abundance pattern in REE
region ~ predictions (exceptions Dm, Eu, Yb: volatility)
 new analytical capabilities offer new possibilities;
RIMS / NanoSIMS: Ba analyses of individual mainstream
SiC grains – compared with model predictions of how
ratios evolve; differ by stellar mass and 13C pocket
barium single grains
also: Fe, Sr, Zr, Mo
Savina
 X-grains of supernova origin – Mo and Ba
towards
100
97
Mo/ Mo
2
r-Mo
(0/3.19)
normal
1
83 normal / 17 burst
(final)
burst
0
0
1
2
96
97
Mo/ Mo
Mo: not r.process
- apparently best
explanation: mix of
normal + “neutron
burst” (Meyer, The,
Clayton)
s
3
Ba: not r-process, not (unadulterated) n burstconsiderably more complex
2.0
burst (final)
mixes 17/83 as for Mo
green: Pellin; red: Marhas
Ba/137Ba
1.5
r (final)
mix (w/final)
135
1.0
normal
mix (w/1a)
0.5
s
0.0
0.0
0.5
1.0
136
Ba/
137
Ba
1.5
 another isotopic signature where neutrons may have
played a role: Xenon-HL in presolar diamonds
150
overabundance [%]
Xenon-HL vs. solar wind xenon
100
Xe-L
Xe-H
Xe-H = likely to
result from a ncapture process

50
0
124
126
128 130 132
mass number
134
136
 extracted H-pattern (assuming zero 130Xe)
quite unlike r-process
 also neutron burst model does not so well
3 .5
3 .0
iX e / 1 3 6 X e
2 .5
r-p ro c e s s
2 .0
1 .5
1 .0
M e y e r 's n b u r s t
0 .5
sep. m odel
d ia m o n d X e
0 .0
130
132
m ass num ber
134
136
 alternative?
normal rprocess with early
separation of
precursors from end
products?
1.0
i
Xe/
136
Xe
0.8
0.6
 r ratios ?
Meyer's n-burst
 mechanism might
work for p (L) part
as well
r-process with
0.4
Howard's
n burst
0.2
separation
Xe-H
0.0
128
mass number
129
130
131
132
133
134
135
136
137
400
(mTe/130Te) [o/oo]
200
 early
separation:
support
from Te
measured
neutron burst
(Howard)
0
-200
neutron burst
(Meyer)
-400
-600
-800
rapid sep.
-1000
p
s
120
122
s
s
r,s s,r
124
126
mass
r
r
128
130
 subcomponent
with
the r-only
isotopes
128, 130 only
 has wrong
r-process (=
normal) ratio
Recent new approaches / technical progress
 resonance ionization (RIMS) for trace elements
in single grains (e.g., Mo, Ba)
 inductively coupled mass spectrometry (ICP-MS):
extends range of elements that can be measured
on large samples with high precision and good
control of mass-dependent fractionation  Maria
 Nano-SIMS: high sensitivity, high lateral
resolution secondary ion mass spectrometry;
 smaller grains, and allows in-situ search for by
high-resolution isotopic mapping  silicates found
Summary:
 meteorites are important standards for
Solar System abundances
 isotope abundance anomalies of various size
/ type / host phase provide a multitude of
information on single processes of
nucleosynthesis
 task: find and interpret them
– import ingredients: stellar models,
nuclear physics