Contradicting previous findings, new research has found that cosmic rays do not pose any hazards at the Earth's surface.
In recent years, research has suggested that "solar particle events" -- spikes in cosmic rays from the sun which sometimes hamper communications or the electric power grid -- may cause congenital birth defects on Earth.
However, the new NASA-funded investigation, published in the Journal of Geophysical Research, found that radiation from solar events is too weak to cause worry at ground level.
"We looked at two different studies. Both of them indicated a connection between cosmic rays and the rate of birth defects," said co-author Professor Adrian Melott from University of Kansas.
"But we have a contradiction. Our estimates suggest that the radiation on the ground from these solar events is very small. And yet the experimental evidence suggests that something is going on that causes birth defects," Mellot added.
Melott and colleagues looked at how cosmic rays from the sun create hazardous "secondaries" by reacting with the Earth's atmosphere.
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Showers of "secondary" high-energy particles are produced when a high-energy cosmic ray strikes Earth's atmosphere.
"Cosmic rays are mostly protons. Some come from the sun, others come from all kinds of violent events all over the universe. Most of the ones that hit the Earth's atmosphere don't reach the ground, but they set off 'air showers' in which other particles are created, and some of them reach the ground," said Mellot.
"The air showers pose the most serious threat for the health of humans and other biology on the Earth's surface via 'ionizing radiation'," according to the researcher.
"Ionizing radiation is any radiation that can tear apart an atom or a molecule. It can affect life in many ways, causing skin cancer, birth defects and other things," he said.
Normally, about one-sixth of the penetrating radiation we get down near sea level is from secondaries from cosmic rays, the researcher said.