Are Earth ice ages created by stars?

Researchers link solar system travel, terrestrial climate

By KEAY DAVIDSON
SAN FRANCISCO CHRONICLE

It might sound preposterous, like astrology, to suggest that galactic events help determine when North America is or isn't buried under immense sheets of ice taller than skyscrapers.

But new research suggests that the coming and going of major ice ages might result partly from our solar system's passage through immense, snakelike clouds of exploding stars in the Milky Way galaxy.

Resembling the curved contrails of a whirling Fourth of July pinwheel, the Milky Way's spiral arms are clouds of stars rich in supernovas, or exploding stars. Supernovas emit showers of charged particles called cosmic rays.

Theorists have proposed that when our solar system passes through a spiral arm, the cosmic rays fall to Earth and knock electrons off atoms in the atmosphere, making them electrically charged, or ionized. Since opposite electrical charges attract each other, the positively charged ionized particles attract the negatively charged portion of water vapor, thus forming large droplets in the form of low-lying clouds.

In turn, the clouds cool the climate and trigger an ice age -- or so theorists suggest.

In that regard, researchers are finding correlations between the timing of Earth's ice ages and epochs when our solar system passed through galactic spiral arms.

The latest evidence appears in a recent issue of Astrophysical Journal. The article is the result of an unusual collaboration between an astronomer, professor Douglas Gies of Georgia State University's Center for High Angular Resolution Astronomy, and a 16-year-old student at Grady High School in Atlanta, John Helsel. They report the results of their effort to determine how the sun has moved through the galaxy over the last half-billion years.

By making a variety of assumptions about the rate of solar motion and the distribution of spiral arms in the galaxy -- which are difficult to map because galactic dust and foreground stars get in the way -- Gies and Helsel conclude that "the sun has traversed four spiral arms at times that appear to correspond well with long-duration cold periods on Earth."

"This," they continue, "supports the idea that extended exposure to the higher cosmic-ray flux associated with spiral arms can lead to increased cloud cover and long ice age epochs on Earth."

Gies and Helsel's article is the long-term result of a project that Helsel began working on "as a science fair project," Gies said. Gies, 50, is a neighbor of Helsel's.

Gies had previously "developed a scheme to model the motion of some massive stars in the galaxy," and when Helsel approached him for guidance on the science fair project, their "conversation quickly focused on studying the sun's motion and encounters with spiral arms in the galaxy."

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