Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...646l.159t&link_type=abstract
The Astrophysical Journal, Volume 646, Issue 2, pp. L159-L162.
Astronomy and Astrophysics
Astronomy
82
Astrochemistry, Nuclear Reactions, Nucleosynthesis, Abundances, Stars: Planetary Systems: Protoplanetary Disks, Solar System: Formation
Scientific paper
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 26Al/27Al 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‰ +/- 0.0038‰) 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.
Baker Joel A.
Bizzarro Martin
Thrane Kristine
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