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

http://ucsdnews.ucsd.edu/newsrel/sci...cmeteorite.asp

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

By Kim McDonald
University of California, San Diego
August 11, 2005

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 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.

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, ??S, 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.