According to NASA’s Goddard Space Flight Center, galactic cosmic rays come from outside the solar system and are made up of subatomic particles accelerated to almost light speed by distant supernova explosions. Cosmic rays cause showers of particles when they hit Earth's atmosphere but they pose their greatest health hazard, radiation, to astronauts in space. They aren’t too healthy for satellites either as a single cosmic ray can disable the unit if one hits an unlucky integrated circuit, NASA said.
"In 2009, cosmic ray intensities have increased 19% beyond anything we've seen in the past 50 years," said Richard Mewaldt of Caltech in a release. "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."
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NASA says the surge is being caused by what it calls a “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 modern times, setting the stage for what Mewaldt calls "a perfect storm of cosmic rays."
Mewaldt also says the solar wind is flagging. "Measurements by the Ulysses spacecraft show that solar wind pressure is at a 50-year low, so the magnetic bubble that protects the solar system is not being inflated as much as usual." A smaller bubble gives cosmic rays a shorter-shot into the solar system. Once a cosmic ray enters the solar system, it must "swim upstream" against the solar wind. Solar wind speeds have dropped to very low levels in 2008 and 2009, making it easier than usual for a cosmic ray to proceed, he stated.
Still the Earth is in no great danger from the cosmic bombardment. The planet's atmosphere and magnetic field combine to form a formidable shield against space radiation, NASA points out.
Earlier this year a NASA-funded study looked to show some of the first clear economic data that quantifies the risk extreme weather conditions in space have on the Earth.