meteorites: Evidence for a single late supernova …Extreme 54Cr-rich oxide grains in meteorites:...
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Extreme 54Cr-rich oxide grains in meteorites: Evidence for a single late supernova injection into the
Solar System
Larry Nittler, Liping Qin, Conel AlexanderJianhua Wang, Rick Carlson
Carnegie Institution of Washington
Frank StadermannWashington University
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Bulk Chondrites
Endemic Cr isotopic anomalies in the Solar System
Acid resistant residues
ε=deviation in parts per 104Qin et al., GCA, 2010 ( see also Rotaru et al, 1992, Podosek et al. 1997, Trinquier et al 2007, etc)
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Origin of Cr isotopic heterogeneity?
• Cosmogenic?–Galactic cosmic ray-induced spallation of Fe in high Fe/Cr materials can produce correlated 54Cr and 53Cr excesses (Qin et al. GCA 2010)
• Nucleosynthetic?– 54Cr made in low-entropy NSE in some SNIa; n-capture in SNII. Carried by presolar SN grains?
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Origin of Cr isotopic heterogeneity?
• Cosmogenic?–Galactic cosmic ray-induced spallation of Fe in high Fe/Cr materials can produce correlated 54Cr and 53Cr excesses (Qin et al. GCA 2010)
• Nucleosynthetic?– 54Cr made in low-entropy NSE in some SNIa; n-capture in SNII. Carried by presolar SN grains?–YES, we have identified sub-µm Cr-oxide grains with extreme 54Cr enrichments in acid residue of Orgueil meteorite (Qin et al., submitted)
• Most likely formed in Type II supernova(e)• Implications for formation of Solar System
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Experimental• Analyze acid-resistant
residue of Orgueil CI meteorite– Very high density of
grains on sample mount
– Mostly sub-µm Cr-rich oxides and some SiC
• NanoSIMS imaging of Cr isotopes (+Ti, Fe)– 500-1000 nm O- beam
– “isotope dilution” significant problem!
52Cr+
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Cr Results• Have identified 10 54Cr-
enriched grains
• 50Cr/52Cr normal
• 53Cr/52Cr normal, except for slight depletion in one grain
Degraded spatial resolution means anomalies are lower limits!
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Dilution of Cr-Isotope Signatures• Estimate true, un-diluted
compositions of grains with simulated ion images based on high-res Cs+ or SEM images
• Grain 7-10:
– Excellent match with “true” 54Cr/52Cr≈54 x Solar!
– Same procedure on other grains also implies very high values
52Cr
0178335665349713289151069812481
Cts
2µm-2002825748571494211711400
2µm
52CrS
0179335875380717489671076112555
Cts
2µm
-2002825748571494211711400
Real 52Cr Sim. 52Cr
Real δ54Cr Sim. δ54Cr
Extreme dilution means that many grains missed in surveys (higher abundance)
Grain 7-10
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Mineralogy
• Use scanning Auger spectroscopy and SIMS to infer grain chemical compositions
7-10 (100 nm)
δ54Cr~53,000 ‰Cr, O, Al
8-3 (80 nm)
δ54Cr> 20,000 ‰Cr, O
6-4 (multiple 100-400 nm Al- or Fe-rich Cr-oxides)
δ54Cr> 11,000 ‰
Al Fe Cr
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Origin of 54Cr-rich Grains?• Grain 7-10
– Inferred 54Cr/52Cr=54 ×
– lower limit ~20 ×
• Cannot be explained by AGB stars (54Cr/52Cr<2×) or spallation
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Origin of 54Cr-rich Grains?• Type Ia supernovae?
– “Normal Ia”: Max 54Cr/52Cr ~ 5 × (Iwamoto et al. 1999, Travaglio et al. 2004)
– “C deflagration Ia”: Much higher 54Cr, but extremely unusual chemistry (unlikely to form oxides) [Meyer et al. 1996, Woosley 1997]
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Origin of 54Cr-rich Grains?• Type II
supernova? – 7-10 composition
consistent with Type II SN 16O-rich zones (s-process)
– Extremely 16O-rich (consistent with meas., but inconclusive)
– Also 53Cr-rich and 50Cr-poor New type of supernova presolar grain
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Supernova oxides/silicates
• 18O-and/or 16O-rich grains likely from SNe-II
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Supernova oxides/silicates
• Majority of grains on single mixing line– Mixing in jets?
• SNe heterogeneous, single mixing line suggests special circumstances, probably a single supernova parent for most grains (Nittler et al. 2008)
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Supernova oxides/silicates
• Majority of grains on single mixing line– Mixing in jets?
• SNe heterogeneous, suggests special circumstances, probably a single supernova parent for most grains (Nittler et al. 2008)– 54Cr rich grains
should lie on same line
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Implications for Solar System
• Heterogeneous distribution of SN grains in solar system?– Bulk variations in Cr isotopes in different
meteorite classes explained by varying amounts of SN 54Cr-rich grains
– 18O-rich (SN) presolar silicates more abundant in cometary (e.g. IDPs) than asteroidal samples (meteorites)
Supports direct injection of SN material into already-formed disk (Ouellette, Desch & Hester 2007, 2010)
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Conclusions• Orgueil acid residue rich in isotopically highly
anomalous presolar oxide grains (54Cr-rich as well as O-anomalous grains)– Isotopic measurements severely affected by poor spatial
resolution• 54Cr-rich grains small (≤100nm) and inferred to have
extreme enrichments (up to >50 x Solar) • C, Ne, O burning zones of Type II SN most likely
source– New type of presolar supernova grain
• Likely significant source of Cr isotope variations in bulk meteorites– Supports model of direct SN injection into early solar
system.