Are Earth ice ages created by stars?

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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."