[meteorite-list] The Birth of Chondrules

From: Peter Marmet <p.marmet_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:55 2005
Message-ID: <42320C0E.E7CDC40_at_dplanet.ch>

Darren Garrison wrote:

> For some reason, "Rednova" always crashed my web browser. Anyone else have that problem?
>

Here it works fine. Here's the text:

Giant Planet Birth Linked to That of Meteorites

Carnegie -- Scientists now believe that the formation of Jupiter, the heavy-weight champion
of the Solar System's planets, may have spawned some of the tiniest and oldest constituents
of our Solar System -- millimeter-sized spheres called chondrules, the major component of
primitive meteorites.

The study, by theorists Dr. Alan Boss of the Carnegie Institution and Prof. Richard H.
Durisen of Indiana University, is published in the March 10, 2005, issue of The
Astrophysical Journal (Letters).

"Understanding what formed the chondrules has been one of biggest problems in the field for
over a century," commented Boss. "Scientists realized several years ago that a shock wave
was probably responsible for generating the heat that cooked these meteoritic components.
But no one could explain convincingly how the shock front was generated in the solar nebula
some 4.6 billion years ago.

These latest calculations show how a shock front could have formed as a result of spiral
arms roiling the solar nebula at Jupiter's orbit. The shock front extended into the inner
solar nebula, where the compressed gas and radiation heated the dust particles as they
struck the shock front at 20,000 mph, thereby creating chondrules," he explained.

"This calculation has probably removed the last obstacle to acceptance of how chondrules
were melted," remarked theorist Dr. Steven Desch of Arizona State University, who showed
several years ago that shock waves could do the job. "Meteoriticists have recognized that
the ways chondrules are melted by shocks are consistent with everything we know about
chondrules. But without a proven source of shocks, they have remained mostly unconvinced
about how chondrules were melted.The work of Boss and Durisen demonstrates that our early
solar nebula experienced the right types of shocks, at the right times, and at the right
places in the nebula to melt chondrules. I think for many meteoriticists, this closes the
deal. With nebular shocks identified as the culprit, we can finally begin to understand what
the chondrules are telling us about the earliest stages of our Solar System's evolution," he
concluded.

"Our calculation shows how the 3-dimensional gravitational forces associated with spiral
arms in a gravitationally unstable disk at Jupiter's distance from the Sun (5 times the
Earth-Sun distance), would produce a shock wave in the inner solar system (2.5 times the
Earth-Sun distance, i.e., in the asteroid belt)," Boss continued. "It would have heated dust
aggregates to the temperature required to melt them and form tiny droplets." Durisen and his
research group at Indiana have independently made calculations of gravitationally unstable
disks that also support this picture.

While Boss is well known as a proponent of the rapid formation of gas giant planets by the
disk instability process, the same argument for chondrule formation works for the slower
process of core accretion. In order to make Jupiter in either process, the solar nebula had
to have been at least marginally gravitationally unstable, so that it would have developed
spiral arms early on and resembled a spiral galaxy.

Once Jupiter formed by either mechanism, it would have continued to drive shock fronts at
asteroidal distances, at least so long as the solar nebula was still around. In both cases,
chondrules would have been formed at the very earliest times, and continued to form for a
few million years, until the solar nebula disappeared. Late-forming chondrules are thus the
last grin of the Cheshire Cat that formed our planetary system.

Boss's research is supported in part by the NASA Planetary Geology and Geophysics Program
and the NASA Origins of Solar Systems Program. The calculations were performed on the
Carnegie Alpha Cluster, the purchase of which was supported in part by the NSF Major
Research Instrumentation Program. Durisen's research was also supported in part by the NASA
Origins of Solar Systems Program.

The Carnegie Institution (www.CarnegieInstitution.org) has been a pioneering force in basic
scientific research since 1902. It is a private, nonprofit organization with six research
departments throughout the U.S. Carnegie scientists are leaders in plant biology,
developmental biology, astronomy, materials science, global ecology, and Earth and planetary
science.


Cheers,

Peter Marmet
Received on Fri 11 Mar 2005 04:22:22 PM PST