Asteroid with an inclusion with high quantities of calcium and aluminium
A calciumâaluminium-rich inclusion or CaâAl-rich inclusion (CAI) is a submillimeter- to centimeter-sized light-colored
calcium- and
aluminium-rich
inclusion found in
carbonaceous chondritemeteorites. The four CAIs that have been
dated using the Pb-Pb chronometer yield a weighted mean age of 4567.30 ± 0.16 Myr.[1][2] As CAIs are the oldest dated solids, this age is commonly used to define the age of the Solar System.
Description
CAIs consist of
minerals that are among the first
solids condensed from the cooling
protoplanetary disk. They are thought to have formed as fine-grained condensates from a high temperature (>1300 K) gas that existed in the protoplanetary disk at early stages of
Solar System formations. Some of them were probably remelted later resulting in distinct coarser textures. The most common and characteristic minerals in CAIs include
anorthite,
melilite,
perovskite, aluminous
spinel,
hibonite, calcic
pyroxene, and
forsterite-rich
olivine.
Using the
lead-lead isotope chronometer (âPbâPb datingâ), the absolute age of four CAIs have been calculated.[1][2] They yield a weighted mean age of 4567.30 ± 0.16 Myr, which is often interpreted as representing the beginning of the formation of the planetary system (so-called âCAI time-zero). It is of note that all four Pb-Pb dated CAIs come from the same group of meteorite (
CV chondrites).
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abConnelly, J. N.; Bizzarro, M.; Krot, A. N.; Nordlund, A.; Wielandt, D.; Ivanova, M. A. (2012-11-02). "The Absolute Chronology and Thermal Processing of Solids in the Solar Protoplanetary Disk". Science. 338 (6107): 651â655.
Bibcode:
2012Sci...338..651C.
doi:
10.1126/science.1226919.
ISSN0036-8075.
PMID23118187.
Bibliography
MacPherson, G. J. (2004) "Calcium-aluminum-rich inclusions in chondritic meteorites." In Treatise on Geochemistry, Volume I, Meteorites, Comets, and Planets, A. M. Davis, edt., Elsevier, New York, pp. 201â246.
ISBN0-08-043751-6
Shukolyukov A., Lugmair G.W. (2002) "Chronology of Asteroid Accretion and Differentiation", pp. 687â695, in Asteroids III, Bottke W.F., Cellino A., Paolicchi P., Binzel R.P., eds., University of Arizona Press (2002),
ISBN0-8165-2281-2