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The new age of the sun.

The new age of the sun

The sun's age, as measured from the time it entered the main sequence of stellar evolution, can't be determined directly. It has to be inferred from the ages of the oldest meteorites -- a difficult task because astronomers must establish a connection between the time of the sun's birth and the formation of meterorites. Recent observations of young stars in star-forming regions are starting to supply that connection.

These young stars, not yet on the main sequence of stellar evolution when they ahieve core temperatures high enough to fuse hydrogen into helium, are surrounded by disks of dust and gas, out of which meteorites form. On the basis of this evidence, David B. Guenther of Yale University in New Haven, Conn., now calculates the sun's age at 4.49 billion years, somewhat less than the 4.7 billion years commonly used in the standard solar model. Guenther reports his results in the April 15 ASTROPHYSICAL JOURNAL.

"The well-determined ages of the meteorites, the theories describing the origin of the solar system, improved to fit recent infrared and radio observations of star-forming regions, and the pre-main-sequence evolutionary calculations have all combined to permit, for the first time, a relatively precise determination of the age of the sun," Guenther says. "Because the error in the age is small and because the solar model is relatively insensitive to small changes in the age, we now have grounds for using the sun's age as a fixed parameter of the standard solar model."

Guenther's calculations show that the 200-million-year difference in age between the old and new estimates has little effect on present theoretical models of how the sun has evolved. Characteristics such as the helium abundance and amount of internal mixing remain relatively unchanged. At the same time, the sunhs new age is more consistent with the age of the oldest known meteorites, which are 4.53 billion years old. Such meteorites would have formed before the sun entered the main sequence of stellar evolution.
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Title Annotation:Astronomy
Publication:Science News
Date:Apr 29, 1989
Words:336
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