TY - JOUR

T1 - Extremely brief formation interval for refractory inclusions and uniform distribution of 26Al in the early solar system

AU - Thrane, Kristine

AU - Bizzarro, Martin

AU - Baker, Joel A.

PY - 2006/8/1

Y1 - 2006/8/1

N2 - Calcium-aluminum-rich inclusions (CAIs) are millimeter-sized refractory objects commonly found in chondritic meteorites and are the oldest solids formed in our solar system. Primary CAI formation may have occurred through condensation and/or evaporation processes near the proto-Sun or, alternatively, during localized events in the asteroid belt. As such, these objects provide us with a unique window into the earliest development of the Sun and into the evolution of the protoplanetary disk. Here we report a 26Al- 26Mg isochron for bulk CAIs from four CV carbonaceous chondrites, which yields an initial 26Al27 Al of (5.85 ± 0.05) × 10-5, suggesting that primary formation of the CV CAIs may have occurred within an interval as brief as 20,000 years. This timescale is inconsistent with the secular evolution of T Tauri stars but may be consistent with CAI formation during the infall stage of the protostellar evolution of the Sun. High-precision Mg isotope measurements of samples from the Earth, Moon, Mars, and bulk chondrite meteorites show that these have identically elevated 26Mg abundances compared to the initial 26Mg abundance (δ26Mg* = -0.0317%0 ± 0.0038% 0) defined by the CAI isochron. This observation unequivocally demonstrates the homogeneous distribution of 26Al within the accretion region of the terrestrial planets. However, the initial 26Mg abundance of CAIs implies a brief history of elevated Al/Mg in CAI precursor material, which may represent primary condensation of refractory silicates and oxides from the solar nebula.

AB - Calcium-aluminum-rich inclusions (CAIs) are millimeter-sized refractory objects commonly found in chondritic meteorites and are the oldest solids formed in our solar system. Primary CAI formation may have occurred through condensation and/or evaporation processes near the proto-Sun or, alternatively, during localized events in the asteroid belt. As such, these objects provide us with a unique window into the earliest development of the Sun and into the evolution of the protoplanetary disk. Here we report a 26Al- 26Mg isochron for bulk CAIs from four CV carbonaceous chondrites, which yields an initial 26Al27 Al of (5.85 ± 0.05) × 10-5, suggesting that primary formation of the CV CAIs may have occurred within an interval as brief as 20,000 years. This timescale is inconsistent with the secular evolution of T Tauri stars but may be consistent with CAI formation during the infall stage of the protostellar evolution of the Sun. High-precision Mg isotope measurements of samples from the Earth, Moon, Mars, and bulk chondrite meteorites show that these have identically elevated 26Mg abundances compared to the initial 26Mg abundance (δ26Mg* = -0.0317%0 ± 0.0038% 0) defined by the CAI isochron. This observation unequivocally demonstrates the homogeneous distribution of 26Al within the accretion region of the terrestrial planets. However, the initial 26Mg abundance of CAIs implies a brief history of elevated Al/Mg in CAI precursor material, which may represent primary condensation of refractory silicates and oxides from the solar nebula.

KW - Astrochemistry

KW - Nuclear reactions, nucleosynthesis, abundances

KW - Planetary systems: protoplanetary disks

KW - Solar system: formation

UR - http://www.scopus.com/inward/record.url?scp=33748051415&partnerID=8YFLogxK

U2 - 10.1086/506910

DO - 10.1086/506910

M3 - Journal article

AN - SCOPUS:33748051415

VL - 646

SP - L159-L162

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2 II

ER -