Chromium isotope systematics of achondrites: Chronology and isotopic heterogeneity of the inner solar system bodies

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Abstract

The standard planetary formation models assume that primitive materials, such as carbonaceous chondrites, are the precursor materials of evolved planetesimals. Past chronological studies have revealed that planetesimals of several hundred kilometers in size, such as the Howardite-Eucrite-Diogenite (HED) parent body (Vesta) and angrite parent body, began their differentiation as early as ∼3 million years of the solar system formation, and continued for at least several million years. However, the timescale of planetesimal formation in distinct regions of the inner solar system, as well as the isotopic characteristics of the reservoirs from which they evolved, remains unclear. Here we present the first report for the precise 53Mn-53Cr ages of monomict ureilites. Chemically separated phases from one monomict ureilite (NWA 766) yielded the Mn-Cr age of 4564.60 ± 0.67 Ma, identical within error to the oldest age preserved in other achondrites, such as angrites and eucrites. The 54Cr isotopic data for this and seven additional bulk ureilites show homogeneous ε54Cr of ∼-0.9, a value distinct from other achondrites and chondrites. Using the ε54Cr signatures of Earth, Mars, and Vesta (HED), we noticed a linear decrease in the ε54Cr value with the heliocentric distance in the inner region of the solar system. If this trend can be extrapolated into the outer asteroid belt, the ε54Cr signatures of monomict ureilites will place the position of the ureilite parent body at ∼2.8 AU. These observations imply that the differentiation of achondrite parent bodies began nearly simultaneously at ∼4565 Ma in different regions of the inner solar system. The distinct ε54Cr value between ureilite and carbonaceous chondrite also implies that a genetic link commonly proposed between the two is unlikely.

Original languageEnglish
Pages (from-to)150-154
Number of pages5
JournalAstrophysical Journal
Volume720
Issue number1
DOIs
Publication statusPublished - Sep 1 2010

Fingerprint

chromium isotopes
achondrites
achondrite
ureilites
chronology
parent body
ureilite
eucrite
solar system
protoplanets
chromium
planetesimal
diogenite
howardite
isotope
carbonaceous chondrites
carbonaceous chondrite
chondrites
signatures
asteroid belts

Keywords

  • Astrochemistry
  • Meteorites, meteors, meteoroids
  • Minor planets, asteroids: general
  • Nuclear reactions, nucleosynthesis, abundances

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics
  • Nuclear and High Energy Physics

Cite this

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title = "Chromium isotope systematics of achondrites: Chronology and isotopic heterogeneity of the inner solar system bodies",
abstract = "The standard planetary formation models assume that primitive materials, such as carbonaceous chondrites, are the precursor materials of evolved planetesimals. Past chronological studies have revealed that planetesimals of several hundred kilometers in size, such as the Howardite-Eucrite-Diogenite (HED) parent body (Vesta) and angrite parent body, began their differentiation as early as ∼3 million years of the solar system formation, and continued for at least several million years. However, the timescale of planetesimal formation in distinct regions of the inner solar system, as well as the isotopic characteristics of the reservoirs from which they evolved, remains unclear. Here we present the first report for the precise 53Mn-53Cr ages of monomict ureilites. Chemically separated phases from one monomict ureilite (NWA 766) yielded the Mn-Cr age of 4564.60 ± 0.67 Ma, identical within error to the oldest age preserved in other achondrites, such as angrites and eucrites. The 54Cr isotopic data for this and seven additional bulk ureilites show homogeneous ε54Cr of ∼-0.9, a value distinct from other achondrites and chondrites. Using the ε54Cr signatures of Earth, Mars, and Vesta (HED), we noticed a linear decrease in the ε54Cr value with the heliocentric distance in the inner region of the solar system. If this trend can be extrapolated into the outer asteroid belt, the ε54Cr signatures of monomict ureilites will place the position of the ureilite parent body at ∼2.8 AU. These observations imply that the differentiation of achondrite parent bodies began nearly simultaneously at ∼4565 Ma in different regions of the inner solar system. The distinct ε54Cr value between ureilite and carbonaceous chondrite also implies that a genetic link commonly proposed between the two is unlikely.",
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author = "Akane Yamakawa and Katsuyuki Yamashita and Akio Makishima and Eizou Nakamura",
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T1 - Chromium isotope systematics of achondrites

T2 - Chronology and isotopic heterogeneity of the inner solar system bodies

AU - Yamakawa, Akane

AU - Yamashita, Katsuyuki

AU - Makishima, Akio

AU - Nakamura, Eizou

PY - 2010/9/1

Y1 - 2010/9/1

N2 - The standard planetary formation models assume that primitive materials, such as carbonaceous chondrites, are the precursor materials of evolved planetesimals. Past chronological studies have revealed that planetesimals of several hundred kilometers in size, such as the Howardite-Eucrite-Diogenite (HED) parent body (Vesta) and angrite parent body, began their differentiation as early as ∼3 million years of the solar system formation, and continued for at least several million years. However, the timescale of planetesimal formation in distinct regions of the inner solar system, as well as the isotopic characteristics of the reservoirs from which they evolved, remains unclear. Here we present the first report for the precise 53Mn-53Cr ages of monomict ureilites. Chemically separated phases from one monomict ureilite (NWA 766) yielded the Mn-Cr age of 4564.60 ± 0.67 Ma, identical within error to the oldest age preserved in other achondrites, such as angrites and eucrites. The 54Cr isotopic data for this and seven additional bulk ureilites show homogeneous ε54Cr of ∼-0.9, a value distinct from other achondrites and chondrites. Using the ε54Cr signatures of Earth, Mars, and Vesta (HED), we noticed a linear decrease in the ε54Cr value with the heliocentric distance in the inner region of the solar system. If this trend can be extrapolated into the outer asteroid belt, the ε54Cr signatures of monomict ureilites will place the position of the ureilite parent body at ∼2.8 AU. These observations imply that the differentiation of achondrite parent bodies began nearly simultaneously at ∼4565 Ma in different regions of the inner solar system. The distinct ε54Cr value between ureilite and carbonaceous chondrite also implies that a genetic link commonly proposed between the two is unlikely.

AB - The standard planetary formation models assume that primitive materials, such as carbonaceous chondrites, are the precursor materials of evolved planetesimals. Past chronological studies have revealed that planetesimals of several hundred kilometers in size, such as the Howardite-Eucrite-Diogenite (HED) parent body (Vesta) and angrite parent body, began their differentiation as early as ∼3 million years of the solar system formation, and continued for at least several million years. However, the timescale of planetesimal formation in distinct regions of the inner solar system, as well as the isotopic characteristics of the reservoirs from which they evolved, remains unclear. Here we present the first report for the precise 53Mn-53Cr ages of monomict ureilites. Chemically separated phases from one monomict ureilite (NWA 766) yielded the Mn-Cr age of 4564.60 ± 0.67 Ma, identical within error to the oldest age preserved in other achondrites, such as angrites and eucrites. The 54Cr isotopic data for this and seven additional bulk ureilites show homogeneous ε54Cr of ∼-0.9, a value distinct from other achondrites and chondrites. Using the ε54Cr signatures of Earth, Mars, and Vesta (HED), we noticed a linear decrease in the ε54Cr value with the heliocentric distance in the inner region of the solar system. If this trend can be extrapolated into the outer asteroid belt, the ε54Cr signatures of monomict ureilites will place the position of the ureilite parent body at ∼2.8 AU. These observations imply that the differentiation of achondrite parent bodies began nearly simultaneously at ∼4565 Ma in different regions of the inner solar system. The distinct ε54Cr value between ureilite and carbonaceous chondrite also implies that a genetic link commonly proposed between the two is unlikely.

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