Title: Planetary
accretion, oxygen isotopes, and the central limit theorem
Author(s): Nuth
JA, Hill HGM
Source: METEORITICS
& PLANETARY SCIENCE 39 (12): 1957-1965 DEC 2004
Document Type: Article
Language: English
Abstract: The
accumulation of presolar dust into increasingly larger aggregates such
as calcium-aluminum-rich inclusions (CAIs) and chondrules, asteroids,
and planets should result in a drastic reduction in the numerical
spread in oxygen isotopic composition between bodies of similar size,
in accord with the central limit theorem. Observed variations in oxygen
isotopic composition are many orders of magnitude larger than would be
predicted by a simple, random accumulation model that begins in a
well-mixed nebula, no matter what size objects are used as the
beginning or end points of the calculation. This discrepancy implies
either that some as yet unspecified but relatively long-lived process
acted on the solids in the solar nebula to increase the spread in
oxygen isotopic composition during each and every stage of
accumulation, or that the nebula was heterogeneous (at least in oxygen)
and maintained this heterogeneity throughout most of its nebular
history. Depending on its origin, large-scale nebular heterogeneity
could have significant consequences for many areas of cosmochemistry,
including the application of well-known isotopic systems to the dating
of nebular events and the prediction of bulk compositions of planetary
bodies on the basis of a uniform cosmic abundance. The evidence
supports a scenario wherein the oxygen isotopic composition of nebular
solids becomes progressively depleted in O-16 With time due to chemical
processing within the nebula, rather than a scenario where O-16-rich
dust and other materials are injected into the nebula, possibly causing
its initial collapse.
KeyWords Plus: SOLAR
NEBULA; INTRAMOLECULAR THEORY; ORDINARY CHONDRITES; GRAINS; METEORITES;
EVOLUTION; COMETS; FRACTIONATION; HETEROGENEITY; CONSTRAINTS
Addresses: Nuth
JA (reprint author), NASA, Goddard Space Flight Ctr, Astrochem Branch,
Code 691, Greenbelt, MD 20771 USA
NASA, Goddard Space Flight Ctr, Astrochem Branch, Greenbelt, MD 20771
USA
Int Space Univ, Illkirch Graffenstaden, F-67400 France
Publisher: METEORITICAL
SOC, DEPT CHEMISTRY/BIOCHEMISTRY, UNIV ARKANSAS, FAYETTEVILLE, AR 72701
USA
Subject Category: GEOCHEMISTRY
& GEOPHYSICS
IDS Number: 901GE
ISSN: 1086-9379
