August 11, 2005
Sun was shining brightly from beginning – study
WASHINGTON (Reuters) - Our Sun was already shining brightly
more than 4.5 billion years ago, as dust and gas was swirling
into what would become the planets of the solar system, U.S.
researchers reported on Thursday.
They said their finding is the first conclusive evidence
that the so-called protosun affected the developing the solar
system by emitting enough ultraviolet energy to catalyze the
formation of organic compounds, water and other elements
necessary for the evolution of life on Earth.
"The basic question was, 'Was the sun on or was it off?"'
said Mark Thiemens of the University of California San Diego,
who led the study.
"There is nothing in the geological record before 4.55
billion years ago that could answer this."
So Thiemens and colleagues studied chemical "fingerprints"
preserved in primitive chondrite meteorites.
Specifically, they report in Friday's issue of the journal
Science, they looked at isotopes, chemical variants, of sulfide
Astronomers believe that wind from the protosun blew matter
from the core into the flat accretion disk -- the layer of gas
and matter from which meteorites, asteroids and planets later
It is no good looking for anything on Earth, which has
undergone extensive change since it was formed. But primitive
meteorites have been less subject to chemical reactions since
they were formed.
The UCSD team determined that a slight excess of one
isotope of sulfur, called 33S, suggests that there were
photochemical reactions going on when the little chunks of
"This measurement tells us for the first time that the sun
was on, that there was enough ultraviolet light to do
photochemistry," Thiemens said in a statement. "Knowing that
this was the case is a huge help in understanding the processes
that formed compounds in the early solar system."
Now the researchers plan to use their technique to look for
other elements in more meteorites and find out more about how
the solar system formed.