[meteorite-list]Sun was Shining when Solar System formed

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Fri Aug 12 17:15:05 2005
Message-ID: <BAY104-F107AEA3682B33B0F95A97AF8BC0_at_phx.gbl>

http://ucsdnews.ucsd.edu/newsrel/science/mcmeteorite.asp

August 11, 2005

UCSD Discovery Suggests 'Protosun' Was Shining
During Formation Of First Matter In Solar System

By Kim McDonald

>From chemical fingerprints preserved in primitive meteorites, scientists at
UCSD have determined that the collapsing gas cloud that eventually became
our sun was glowing brightly during the formation of the first material in
the solar system more than 4.5 billion years ago.

Their discovery, detailed in a paper that appears in the August 12 issue of
Science, provides the first conclusive evidence that this “protosun” played
a major role in chemically shaping the solar system by emitting enough
ultraviolet energy to catalyze the formation of organic compounds, water and
other compounds necessary for the evolution of life on Earth.


Protosun at the center of the solar nebula
Credit: NASA
Scientists have long argued whether the chemical compounds created in the
early solar system were produced with the help of the energy of the early
sun or were formed by other means.

“The basic question was, Was the sun on or was it off?” says Mark H.
Thiemens, Dean of UCSD’s Division of Physical Sciences and chemistry
professor who headed the research team that conducted the study. “There is
nothing in the geological record before 4.55 billion years ago that could
answer this.”

Vinai Rai, a postdoctoral fellow working in Thiemens’ lab, came up with a
solution, developing an extremely sensitive measurement that could answer
the question. He searched for chemical fingerprints of the high-energy wind
that emanated from the protosun and became trapped in the isotopes, or
forms, of sulfide found in four primitive groups of meteorites, the oldest
remnants of the early solar system. Astronomers believe this wind blew
matter from the core of the rotating solar nebula into its pancake-like
accretion disk, the region in which meteorites, asteroids and planets later
formed.

Applying a technique Thiemens developed five years ago to reveal details
about the Earth’s early atmosphere from variations in the oxygen and sulfur
isotopes embedded in ancient rocks, the UCSD chemists were able to infer
from sulfides in the meteorites the intensity of the solar wind and, hence,
the intensity of the protosun. They conclude in their paper that the slight
excess of one isotope of sulfur, ³³S, in the meteorites indicated the
presence of “photochemical reactions in the early solar nebula,” meaning
that the protosun was shining strongly enough to drive chemical reactions.

“This measurement tells us for the first time that the sun was on, that
there was enough ultraviolet light to do photochemistry,” says Thiemens.
“Knowing that this was the case is a huge help in understanding the
processes that formed compounds in the early solar system.”

Astronomers believe the solar nebula began to form about 5 billion years ago
when a cloud of interstellar gas and dust was disturbed, possibly by the
shock wave of a large exploding star, and collapsed under its own gravity.
As the nebula’s spinning pancake-like disk grew thinner and thinner,
whirlpools of clumps began to form and grow larger, eventually forming the
planets, moons and asteroids. The protosun, meanwhile, continued to contract
under its own gravity and grew hotter, developing into a young star. That
star, our sun, emanated a hot wind of electrically charged atoms that blew
most of the gas and dust that remained from the nebula out of the solar
system.

Planets, moons and many asteroids have been heated and had their material
reprocessed since the formation of the solar nebula. As a result, they have
had little to offer scientists seeking clues about the development of the
solar nebula into the solar system. However, some primitive meteorites
contain material that has remained unchanged since the protosun spewed this
material from the center of the solar nebula more than 4.5 billion years
ago.

Thiemens says the technique his team used to determine that the protosun was
glowing brightly also can be applied to estimate when and where various
compounds originated in the hot wind spewed out by the protosun.

“That will be the next goal,” he says. “We can look mineral by mineral and
perhaps say here’s what happened step by step.”

The UCSD team’s study was financed by a grant from the National Aeronautics
and Space Administration.
Received on Fri 12 Aug 2005 05:15:01 PM PDT