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Sun's 8.2-billion-year-old twin found

  • sunstwin2.jpg

    This image tracks the life of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant star on the right. (ESO/M. Kornmesser)

  • SUNSTWIN.jpg

    This image shows solar twin HIP 102152, a star located 250 light-years from Earth in the constellation of Capricornus (The Sea Goat). (ESO/Digitized Sky Survey 2. Ack: Davide De Martin)

About 250 light-years away in the constellation Capricornus (The Sea Goat) lies a star that looks awfully familiar.

Known as HIP 102152, the star is a virtual twin of our sun, which in and of itself is not so unusual. But HIP 102152 is older than our 4.6-billion-year old sun -- by nearly 4 billion years, making it the oldest solar twin found to date.

"It is important for us to understand our sun in the proper context of stellar astronomy and to identify which of its properties are unique and normal, to predict what its fate may someday be," astronomer TalaWanda Monroe, a postdoctoral fellow at the University of San Paulo in Brazil, wrote in an email to Discovery News.

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With human lifespans so limited, seeing the sun in context means astronomers must find stars with similar mass, chemical composition, temperature and other characteristics. From that, they can then extrapolate information about our sun, such as how bright it shined in its youth and how different its radiation may be in the future.

"HIP 102152 is an ideal star to anchor the end of the timeline," Monroe said.

Stars like the sun last about 10 billion years before running out of hydrogen fuel for their thermonuclear reactions. They then cool and expand into what is known as a "red giant" phase.

HIP 102152 may be like the sun in another way as well. Unlike other solar twins, chemical analysis of HIP 102152's light shows a good match to the sun's, including a telltale sign of possible rocky planets.

Scientists found elements common in dust and meteorites missing from HIP 102152's light -- "a strong hint ... that the elements may have gone into making rocky bodies and/or planets" around the star," Monroe wrote.

So far, attempts to search for any orbiting planets have not been successful.

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The group also was able to make a direct tie between the amount of lithium in a star and the star’s age.

Some previous studies suggested a low lithium content may indicate the presence of giant planets, said astronomer Jorge Melendez, also with the University of San Paulo.

The new research shows that as a solar-type star ages, its lithium content decreases.

"We could use lithium to estimate the age of a star, something that is very difficult to obtain," Melendez wrote in an email to Discovery News.

The discovery, made with the European Southern Observatory's Very Large Telescope, was unveiled at press conference on Wednesday and is the subject of an upcoming paper in Astrophysical Journal Letters.