Astronauts travelling to Mars or other deep space missions may be at a two-fold higher risk of developing cancer than previously assumed, due to exposure to cosmic rays outside the protection of Earth's magnetic field, a new study warns.
The findings, published in the journal Scientific Reports, effectively doubled the cancer risk for a human mission to Mars.
Previous studies have shown the health risks from galactic cosmic ray exposure to astronauts include cancer, central nervous system effects, cataracts, circulatory diseases and acute radiation syndromes.
Cosmic rays, such as iron and titanium atoms, heavily damage the cells they traverse because of their very high rates of ionisation.
Conventional risk models used by NASA and others assume DNA damage and mutation are the cause of radiation cancers.
This is based on studies at high doses where all cells are traversed by heavy ions one or more times within much shorter-time periods than will occur during space missions.
"Exploring Mars will require missions of 900 days or longer and includes more than one year in deep space where exposures to all energies of galactic cosmic ray heavy ions are unavoidable," said Francis Cucinotta, a researcher at the University of Nevada, Las Vegas in the US.
"Current levels of radiation shielding would, at best, modestly decrease the exposure risks," Cucinotta said.
In the new findings, a model, where cancer risk arises in bystander cells close to heavily damaged cells, is shown to lead to a two-fold or more increase in cancer risk compared to the conventional risk model for a Mars mission.
"Galactic cosmic ray exposure can devastate a cell's nucleus and cause mutations that can result in cancers," Cucinotta said.
"We learned the damaged cells send signals to the surrounding, unaffected cells and likely modify the tissues' microenvironments," he said.
"Those signals seem to inspire the healthy cells to mutate, thereby causing additional tumours or cancers," he added.
The findings show a tremendous need for additional studies focused on cosmic ray exposures to tissues that dominate human cancer risks, and that these should begin prior to long-term space missions outside the Earth's geomagnetic sphere.