The Formation Conditions of Chondrules and Chondrites
C. M. O'D. Alexander,1*
J. N. Grossman,2
D. S. Ebel,3
F. J. Ciesla1
Chondrules, which are roughly millimeter-sized silicate-rich
spherules, dominate the most primitive meteorites, the chondrites.
They formed as molten droplets and, judging from their abundances
in chondrites, are the products of one of the most energetic
processes that operated in the early inner solar system. The
conditions and mechanism of chondrule formation remain poorly
understood. Here we show that the abundance of the volatile
element sodium remained relatively constant during chondrule
formation. Prevention of the evaporation of sodium requires
that chondrules formed in regions with much higher solid densities
than predicted by known nebular concentration mechanisms. These
regions would probably have been self-gravitating. Our model
explains many other chemical characteristics of chondrules and
also implies that chondrule and planetesimal formation were
linked.
2 U.S. Geological Survey, Reston, VA 20192, USA.
3 American Museum of Natural History, New York, NY 10024, USA.
* To whom correspondence should be addressed. E-mail: alexande{at}dtm.ciw.edu
