[meteorite-list] Oddball Meteorites Hold Clues To Stars' Birth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:38 2004
Message-ID: <200103110415.UAA00707_at_zagami.jpl.nasa.gov>

http://starbulletin.com/2001/03/09/news/story7.html

Oddball meteorites hold clues to stars' birth
By Helen Altonn
Honolulu Star-Bulletin
March 9, 2001

     University of Hawaii researchers have raised new questions about
     the solar system's creation with analysis of two unusual
     meteorites.

     Most meteorites found on Earth were believed to be fragments of
     asteroids formed when the solar system was created about 4.56
     billion years ago.

     But the UH study, reported recently in the journal Science, takes
     a different twist.

     The UH researchers, led by Alexander Krot, Hawaii Institute of
     Geophysics and Planetology associate researcher, examined two rare
     meteorite specimens.

     HH 237, about the size of a grapefruit, was recovered from
     northern Africa. QUE 94411, a walnut-size sample, was discovered
     in an Antarctica mountain range. Both were loaded with pristine
     iron and nickel.

     Krot's collaborators included institute Director Klaus Keil;
     Anders Meibom, former institute scientist now at Stanford
     University; Sara S. Russell and Timothy E. Jeffries of the Natural
     History Museum in London; and Conel M. Alexander of the Carnegie
     Institute of Washington's Department of Terrestrial Magnetism.

     Krot participated in the expedition that found the primitive
     meteorite in Antarctica in 1991, and the UH team and colleagues
     discovered its preserved 4.56 billion-year-old metal grains. They
     were the first solids found in the solar system.

     That discovery was reported in Science last May. The group's
     latest findings were published in the March 2 issue.

     Discussing them in interviews, Krot and Keil explained that
     primitive meteorites, or chondrites, contain thousands of tiny
     particles known as chondrules.

     As the oldest rocks in the solar system, chondrites tell of the
     solar system's origin, Keil said. "They contain these
     millimeter-sized spheres, chondrules, named after the Greek word
     for grains."

     Most meteorites were thought to have formed in the asteroid belt
     region between the Jupiter and Mars orbits, about 140 million
     miles from Earth, the scientists said.

     It's believed chondrules started as dust balls that were melted by
     a heating mechanism that briefly raised the asteroid belt's
     temperatures -- then just below 700 degrees -- to about 3,000
     degrees, Keil said.

     "Imagine a rain of little dust balls, and some heating mechanism.
     We're not clear what that was," he said, noting ideas that it
     could have been a burst of lightning or shock waves.

     "They cooled relatively quickly and accreted to form parent bodies
     of meteorites that we have today -- the asteroids," Keil said.

     However, chondrules in the two meteorites discovered in Antarctica
     and Africa did not form by that process, he said.

     Instead of forming in the asteroid belt, Krot said, "We think they
     formed in a place close to the sun. It tells us there was
     significant mixing of materials in the solar system when the sun
     formed."

     Chemical analysis of the two meteorites suggests the metal grains
     formed at very high temperatures in the solar nebula, the
     scientists said. The chondrules condensed from very hot gas into
     liquid droplets that were quickly blown away from the sun to
     cooler regions, they said.

     The team's findings support a theory proposed in 1996 by
     astronomer Frank Shu of the University of California based on
     images from the Hubble Space Telescope.

     Hubble allowed scientists for the first time to observe the birth
     of new stars elsewhere in the Milky Way. They found most young
     stars are created from enormous disks of whirling gas and dust.

     As the disk contracts, it rotates faster and faster, funneling
     tons of interstellar dust toward the center, where temperatures
     reach 3,000 degrees or more -- hot enough to melt metal and
     vaporize most solids.

     The rotating disk also produces enormous gas jets capable of
     launching debris far into space at speeds of hundreds of miles per
     second.

     Based on these Hubble images, Shu proposed that chondrules in
     Earth's solar system were created near the hot central disk of a
     newly emerging sun -- not in the relatively cool asteroid belt
     hundreds of millions of miles away.

     Shu suggested that dust particles were melted by the sun, then
     launched into space by powerful gas jets and solar wind -- some
     landing in the asteroid belt and others ending up as materials
     forming Earth, Mars and other planets.

     The UH study provided the first evidence to support Shu's theory
     of chondrule and star formation.

     The next goal will be to date all the components of the
     meteorites, Krot said. "Basically, using this technique, we can
     date components from 1 to 2 million years after the formation of
     our sun."

     Aside from exploring the first few million years of the solar
     system, Keil said the most exciting thing in the development is
     that the scientists have bridged a gap between cosmochemistry --
     the study of extraterrestrial materials -- and astrophysics.

     "We now can ... provide some real hard evidence for astrophysical
     theories."
Received on Sat 10 Mar 2001 11:15:45 PM PST