August 11, 2005

Sun Was Shining Brightly from Beginning

WASHINGTON -- 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 compounds.

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 formed.

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 meteorite coalesced.

"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.


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