[meteorite-list] Meteorites Hold Clues To Early Solar System

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:54:07 2004
Message-ID: <200202211621.IAA10291_at_zagami.jpl.nasa.gov>

http://starbulletin.com/2002/02/19/news/story13.html

Meteorites Hold Clues To Early Solar System
By Helen Altonn (haltonn_at_starbulletin.com)
Honolulu Star-Bulletin
February 19, 2002

UH scientists report that planets may have formed very quickly

Mineral findings in two meteorites studied by University of Hawaii
scientists and mainland colleagues may change thinking about the solar
system's age.

If their analysis of two major components is correct, "the whole idea about
the chronology of the solar nebula can be wrong," said Alexander Krot,
associate researcher at the Hawaii Institute of Geophysics and Planetology.

The researchers have dated one component at 4.568 billion years, plus or
minus 1 million or 2 million years, and they will try next to define the
absolute age of the second major component.

"If we find they're the same," Krot said, "basically it will tell us
probably the disk around the sun existed mostly only 1 million years, and
planets formed very quickly."

Krot and HIG planetary scientist Edward Scott collaborated with Kevin
McKeegan of the University of California-Los Angeles, Laurie Leshin of
Arizona State University and Glenn MacPherson of the U.S. National Museum of
Natural History.

They analyzed particles from meteorites Efremovka, landing in Russia in
1962, and Vigarano, which landed in Italy in 1910. They are fresher than
other meteorites, the scientists said, because they were in part of an
asteroid that was not so weathered.

A paper describing their findings appears in the Feb. 8 issue of the journal
Science.

Scott said the primitive meteorites (chondrites) contain little particles
the researchers think were formed in the dust and gas disk (the solar
nebula) that formed at the same time as the sun, and from which all planets
were formed.

Two of the major components are calcium-aluminum-rich inclusions (CAIs) and
chondrules. CAIs contain abundant calcium and aluminum oxides, while
chondrules are richer in iron, magnesium and silicon oxides.

If they can date the origin of the CAIs and chondrules, Krot said, "we can
say when they formed and what is the age of our solar system."

Originally, it was thought the disk lasted 50 million years around the sun
before planets formed, he said. That shrank to 10 million years, and now
people are talking about the solar nebula lasting 1 million to 5 million
years, he said.

According to their analysis, the two major components formed in different
parts of the solar nebula and have very different gas composition.

Krot said they found differences in isotopes (oxygen atoms) in regions where
the components formed. People generally have associated those differences
with age differences, saying CAIs formed first and chondrules later, he
said.

But their findings potentially show the isotopic differences have nothing to
do with age, he said.

"It could just be spatial differences, so regions where the two components
formed existed at the same time, but isotopic signatures of the two regions
were different."

Scott said if you pick up meteorite rocks from Mars or the asteroid belt,
the three oxygen isotopes are proportionately different.

Techniques in their field allow them to define age within 1 million years,
Krot said, explaining the next step is to define the absolute age of
chondrules.

The fact that the components have isotopic differences does not mean they
formed at different times, he said. One explanation may be that CAIs formed
close the sun and chondrules formed further away, he added.

Many people have been studying meteorites 30 to 40 years trying to
understand how the major components formed, Scott said.

"It has been a tough struggle, particularly because we have to imagine
what's happening.

"Now, we're getting a lot more information from astronomers who can see more
how stars are forming. That's where we hope the breakthrough is coming, so
we can relate in more detail what we're seeing to what astronomers are
telling us about stars."
Received on Thu 21 Feb 2002 11:21:53 AM PST