"In 2009, cosmic ray intensities have increased 19 percent beyond anything we've seen in the past 50 years," said Richard Mewaldt of Caltech. "The increase is significant, and it could mean we need to re-think how much radiation shielding astronauts take with them on deep-space missions."
The surge, which poses no threat to Earth, was detected by NASA's ACE (Advanced Composition Explorer) spacecraft.
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."
An alternate but related hypothesis of ice ages suggests that Earth occasionally passes through huge interstellar clouds of hydrogen gas. Such clouds are common in the spiral arms. According to this hypothesis, the interstellar clouds chemically soak up oxygen molecules in Earth's atmosphere, dramatically lowering the levels of the gas ozone.
Voyager Nears Local Fluff
Our solar system is plunging through a vast cloud of wispy gas called the local interstellar cloud, also known as the “Local Fluff.” About 30 light-years wide, the Fluff is made of 6,000°C hydrogen and helium. The Fluff is about twice as dense as the interstellar meduim surrounding it, and what holds it together has been a mystery—until now, thanks to a discovery by JPL’s twin Voyager spacecraft.
The gas in the Local Fluff has a density of approximately 0.1 atoms per cubic centimeter, approximately double that of the galactic interstellar medium and 20 times that of the gas in the Local Bubble.
Local Chimney and Superbubbles
Some wisps of the Local Fluff's denser gas may already have blown into the Solar System earlier (possibly 33,000 and 60,000 years ago) (Priscilla Chapman Frisch, 1997). Astronomers hypothsize that such gas clouds can suppress the Solar Wind so that interstellar gas and dust enters the Solar System in quantities great enough to affect the Sun and life on Earth. At the moment, a powerful stellar wind from the young OB stellar associations of the Local Bubble's expanding neighbor, the Loop I Bubble, is pushing the Local Fluff aside (at the rate of 12 miles, or 20 km, per second). That expanding bubble, however, is also pushing other clouds of gas towards the Solar System (Astronomy Picture of the Day).