StarDate: January 21, 2010

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Most of the elements on Earth were created in the stars. A good example is tin, a metal that was forged by nuclear reactions in the hearts of red giants -- aging stars that are bigger, brighter, and cooler than the Sun.

A couple of red giants are on fine display tonight. Aldebaran, the "eye" of Taurus, the bull, is high in the south at nightfall. And Pollux, one of the "twins" of Gemini, is in the east, well above the planet Mars. Both stars look orange, which helps them stand out.

The nuclear reactions inside a red giant can release neutrons -- subatomic particles with no electric charge. When the neutrons strike the nuclei of iron atoms deep inside the star, they stick. That makes the iron nuclei grow heavier. Some of them become so heavy that they form tin, which is about twice as heavy as iron.

Because this process occurs slowly, scientists call it the s-process -- "s" for "slow." The s-process created most of the tin that's present on Earth. It also created some of the other heavy elements, like lead.

Some of these heavy elements enter the red giant's outer layers -- its atmosphere. At the end of its life, a red giant casts this atmosphere into space, like a dandelion going to seed. The tin, lead, and other elements the star has manufactured escape into space -- ready to enrich the clouds of gas and dust that give birth to new stars and planets, which inherit these heavy elements for their own.

Script by Ken Croswell, Copyright 2009

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