Earth is being bombarded by powerful cosmic rays from deep in the galaxy because the Sun’s natural shields are down, NASA reports.

The level of space radiation is nearly a fifth higher this year than at any time since the dawn of the space age 50 years ago.

The tiny, energetic, sub-atomic  particles – smaller than atoms but flying at close to the speed of light – can pass completely through solid objects. They are released by massive explosions such as exploding stars called supernovae.

Usually the solar wind – a stream of energy from the sun – together with its magnetic field act like a bubble called the heliosphere around the solar system to protect planets from much of the bombardment. But activity on the sun is at its weakest for around a century, weakening this protective shield.

The Earth has its own natural shield too – our own magnetic field helps deflect radiation from space and experts insist that there is no danger from the rise in cosmic rays.

But if they remain at a high level, it would be a real hazard for astronauts embarking on a mission to Mars. Space engineers would need to provide plenty of physical shielding on their spacecraft to protect them from potentially deadly doses of radiation.

The soaring numbers of cosmic rays were detected by instruments aboard NASA ‘s unmanned Advanced Composition Explorer spacecraft from a position nearly a million miles away between Earth and the sun.

Richard Mewaldt, of the Californian Institute of Technology, says the stage is set for “a perfect storm of cosmic rays.” He added: “In 2009, cosmic ray intensities have increased 19% beyond anything we’ve seen in the past 50 years. 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.”

Read NASA’s report here.

Picture: A diagram illustrating how the heliophere acts like a protective bubble around the solar system. (Credit: NASA). 

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