NASA spacecraft are measuring record-high levels of cosmic rays, a side effect of the deepest solar minimum in nearly a century. The cosmic ray storm appears to be intensifying, say researchers, and the peak may be yet to come.

According to sensors on NASA's Advanced Composition Explorer spacecraft, galactic cosmic rays have just hit a 50-year high.

The cause of the surge is solar minimum, a deep lull in solar activity that began around 2007 and continues today. Researchers have long known that cosmic rays go up when solar activity goes down. Right now solar activity is as weak as it has been in nearly a century.

Galactic cosmic rays are high-energy particles that are accelerated to almost light speed by distant supernova explosions. They flow into our solar system from far away in the galaxy. They are mostly pieces of atoms: protons, electrons and atomic nuclei that have had all of the surrounding electrons stripped during their high-speed passage through the galaxy.

The sun's magnetic field is our first line of defense against these highly charged, energetic particles. The entire solar system from Mercury to Neptune and beyond is surrounded by a bubble of magnetism called "the heliosphere." It springs from the sun's inner magnetic dynamo. When a cosmic ray tries to enter the solar system, it must fight through the heliosphere's outer layers; and if it makes it inside, there is a thicket of magnetic fields waiting to scatter and deflect the cosmic intruder.

At times of low solar activity, this natural shielding is weakened, and more cosmic rays are able to reach the inner solar system.

Our planet's atmosphere and magnetic field provide some defense against the extra cosmic rays. However, they do pose a health hazard to astronauts. And a single cosmic ray can disable a satellite if it hits an unlucky integrated circuit.

Doug Oster writes a blog, "Growing With Doug," exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.