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

[Pete Pete]

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.