[meteorite-list] Oldest Objects in Solar System Indicate a Turbulent Beginning

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 14 Mar 2011 17:37:58 -0700 (PDT)
Message-ID: <201103150037.p2F0bwiN022848_at_zagami.jpl.nasa.gov>

https://www.llnl.gov/news/newsreleases/2011/Mar/NR-11-03-02.html

Oldest objects in solar system indicate a turbulent beginning
For immediate release: 03/03/2011 | NR-11-03-02

Anne M Stark
Lawrence Livermore National Laboratory
(925) 422-9799, stark8 at llnl.gov

LIVERMORE, Calif. -- Scientists have found that calcium, aluminum-rich
inclusions (CAIs), some of the oldest objects in the solar system,
formed far away from our sun and then later fell back into the mid-plane
of the solar system.

The findings may lead to a greater understanding of how our solar system
and possibly other solar systems formed and evolved.

CAIs, roughly millimeter- to centimeter in size, are believed to have
formed very early in the evolution of the solar system and had contact
with nebular gas, either as solid condensates or as molten droplets.
Relative to planetary materials, CAIs are enriched with the lightest
oxygen isotope and are believed to record the oxygen composition of
solar nebular gas where they grew. CAIs, at 4.57 billion years old, are
millions of years older than more modern objects in the solar system,
such as planets, which formed about 10-50 million years after CAIs.

Using Lawrence Livermore's NanoSIMS (nanometer-scale secondary-ion mass
spectrometer) -- an instrument that can analyze samples with
nanometer-scale spatial resolution -- LLNL scientists in conjunction
with NASA Johnson Space Center, University of California, Berkeley and
the University of Chicago measured the concentrations of oxygen isotopes
found in the CAIs.

In the recent research, the team studied a specific CAI found in a piece
of the Allende meteorite. Allende is the largest carbonaceous chondrite
meteorite ever found on Earth. It fell to the ground in 1969 over the
Mexican state of Chihuahua and is notable for possessing abundant CAIs.

Their findings imply that CAIs formed from several oxygen reservoirs,
likely located in distinct regions of the solar nebula. CAIs travelled
within the nebula by lofting outward away from the sun and then later
falling back into the mid-plane of the solar system or by spiraling
through shock waves around the sun.

Through oxygen isotopic analysis, the team found that rims surrounding
the CAI show that late in the CAI's evolution, it was in a nebular
environment distinct from where it originated and closer in composition
to the environment in which the building materials of the terrestrial
planets formed.

"Allende is this very unusual meteorite with all these wonderful
inclusions (CAIs)," said Ian Hutcheon, one of the LLNL scientists on the
team. "The isotopic measurements indicate that this CAI was transported
among several different nebular oxygen isotopic reservoirs, arguably as
it passed through into various regions of the protoplanetary disk."

A protoplanetary disk is an area of dense gas surrounding a newly formed
star. In this case, the CAI formed when our star was quite young.

"It is particularly interesting in understanding the formation and
dynamics of our solar system's protoplanetary disk (and protoplanetary
disks in general)," said Justin Simon of NASA Johnson Space Center and
lead author of a paper appearing in the March 4 issue of the journal
Science.

The new observations, "support early and short-lived fluctuations of the
environment in which CAIs formed, either due to transport of the CAIs
themselves to distinct regions of the solar nebula or because of varying
gas composition near the proto-sun", Hutcheon said.

Other Livermore researchers include Jennifer Matzel, Erick Ramon and
Peter Weber.
Received on Mon 14 Mar 2011 08:37:58 PM PDT