Demonstration of <sup>26</sup> Mg excess in Allende and evidence for <sup>26</sup> Al

Lee, Typhoon; Papanastassiou, D. A.; Wasserburg, G. J.

doi:10.1029/gl003i001p00041

Cited by 226 publications

(163 citation statements)

References 18 publications

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“…The thermal model also does not include the potential influence of an overlying regolith to reduce the thermal diffusivity. Two previous estimates of 26 Al heating of meteorite parent bodies 64,65 reported much higher temperatures than those calculated here, most likely owing to the differences in the assumed physical properties such as the thermal diffusivity (previous studies assumed values of o0.01) and the water/rock ratio (assumed to be zero in the previous studies). We note that increasing the water/rock ratio not only increases the amount of energy required to heat the parent body to a given temperature (ice has a higher heat capacity than rock) but also reduces the amount of 26 Al (per unit mass) available to produce heat as water does not contain any 26 Al.…”

Section: Methodscontrasting

confidence: 70%

Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite

et al. 2015

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Chronology of aqueous activity on chondrite parent bodies constrains their accretion times and thermal histories. Radiometric 53 Cr dating has been successfully applied to aqueously formed carbonates in CM carbonaceous chondrites. Owing to the absence of carbonates in ordinary (H, L and LL), and CV and CO carbonaceous chondrites, and the lack of proper standards, there are no reliable ages of aqueous activity on their parent bodies. Here we report the first 53 Mn-53 Cr ages of aqueously formed fayalite in the L3 chondrite Elephant Moraine 90161 as 2:4 þ 1:8 À 1:3 Myr after calcium-aluminium-rich inclusions (CAIs), the oldest Solar System solids. In addition, measurements using our synthesized fayalite standard show that fayalite in the CV3 chondrite Asuka 881317 and CO3-like chondrite MacAlpine Hills 88107 formed 4:2 þ 0:8 À 0:7 and 5:1 þ 0:5 À 0:4 Myr after CAIs, respectively. Thermal modelling, combined with the inferred conditions (temperature and water/rock ratio) and 53 Cr ages of aqueous alteration, suggests accretion of the L, CV and CO parent bodies B1.8 À 2.5 Myr after CAIs.

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Section: Methodscontrasting

confidence: 70%

Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite

et al. 2015

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“…In particular, Gray et al [3] found one inclusion having the lowest a TSr/a6Sr ratio ever seen in any solar system object. In addition, the extreme antiquity of these inclusions is further demonstrated by the presence in them of excess 26Mg attributed to in-situ decay of 7.4 × l0 s yr Z6A1 [10,11].…”

Section: Age Of Allende Inclusionsmentioning

confidence: 99%

The case for an unfractionated244Pu/238U ratio in high-temperature condensates

Ganapathy

Grossman

1976

Earth and Planetary Science Letters

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The coarse-g~ained, Ca-rich inclusions in the AUende meteorite are the highest-temperature condensates from the cooling solar nebula and, as such, the oldest solid objects in the solar system. All refractory elements with condensalion points above the accretion temperature of the inclusions whose eoneentrarions in them have been measured are seen to be present in the inclusions in unfractionated proportion to one another relative to C1 ehondrites when data ate averaged for a large number of inclusions. Observational data for U and theoretical data for both U and Pu'suggest that these elements exhibited refractory behavior in the solar nebula. An experiment is proposed in which fissiogenic Xe and U contents are measured in a suite of these inclusions to obtain the 244pu/238U ratio of the solar system at the time of initial condensation with an uncertainty of + 15%.

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“…Its widespread presence in the early solar system has been identified in the CAIs and chondrules (e.g. Lee et al 1976;MacPherson et al 1995;Bizzarro et al 2004). An initial 26 Al/ 27 Al abundance ratio of 5 × 10 −5 is suggested at the time of CAI formation (canonical value) that is based on measurements of CAIs in meteorites (MacPherson et al 1995).…”

Section: Introductionmentioning

confidence: 99%

Differentiation and core formation in accreting planetesimals

Neumann

Breuer

Spohn

2012

A&A

114

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Aims. The compositions of meteorites and the morphologies of asteroid surfaces provide strong evidence that partial melting and differentiation were widespread among the planetesimals of the early solar system. However, it is not easily understood how planetesimals can be differentiated. To account for significantly smaller radii, masses, gravity and accretion energies early, intense heat sources are required, e.g. the short-lived nuclides 26 Al and 60 Fe. Here, we investigate the process of differentiation and core formation in accreting planetesimals taking into account the effects of sintering, melt heat transport via porous flow and redistribution of the radiogenic heat sources. Methods. We use a spherically symmetric one-dimensional model of a partially molten planetesimal consisting of iron and silicates, which considers the accretion by radial growth. The common heat conduction equation has been modified to consider also melt segregation. In the initial state, the planetesimals are assumed to be highly porous and consist of a mixture of Fe,Ni-FeS and silicates consistent to an H-chondritic composition. The porosity change due to the so called hot pressing is simulated by solving a corresponding differential equation. Magma segregation of iron and silicate melt is treated according to the flow in porous media theory by using the Darcy flow equation and allowing a maximal melt fraction of 50%. Results. We show that the differentiation in planetesimals depends strongly on the formation time, accretion duration, and accretion law and cannot be assumed as instantaneous. Iron melt segregation starts almost simultaneously with silicate segregation and lasts between 0.4 and 10 Ma. The degree of differentiation varies significantly and the most evolved structure consists of an iron core, a silicate mantle, which are covered by an undifferentiated but sintered layer and an undifferentiated and unsintered regolith -suggesting that chondrites and achondrites can originate from the same parent body.

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Demonstration of ²⁶ Mg excess in Allende and evidence for ²⁶ Al

Cited by 226 publications

References 18 publications

Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite

Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite

The case for an unfractionated244Pu/238U ratio in high-temperature condensates

Differentiation and core formation in accreting planetesimals

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Demonstration of 26 Mg excess in Allende and evidence for 26 Al

Cited by 226 publications

References 18 publications

Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite

Early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by fayalite

The case for an unfractionated244Pu/238U ratio in high-temperature condensates

Differentiation and core formation in accreting planetesimals

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Demonstration of ²⁶ Mg excess in Allende and evidence for ²⁶ Al