New York, Jun 6 (IANS): Astronauts travelling to Mars or on long-term missions outside the protection of the Earth's magnetic field would face much higher cancer risk than conventional risk models suggest, a study says.

"Exploring Mars will require missions of 900 days or longer and include more than one year in deep space where exposures to all energies of galactic cosmic ray heavy ions are unavoidable," said one of the researchers, Francis Cucinotta, scientist at University of Nevada, Las Vegas.

"Galactic cosmic ray exposure can devastate a cell's nucleus and cause mutations that can result in cancers," Cucinotta explained.

In these new findings published in the journal Scientific Reports, a non-targetted effect model -- where cancer risk arises in bystander cells close to heavily damaged cells -- was shown to lead to a two-fold or more increase in cancer risk compared to the conventional risk model for a Mars mission.

"We learned the damaged cells send signals to the surrounding, unaffected cells and likely modify the tissues' microenvironments. Those signals seem to inspire the healthy cells to mutate, thereby causing additional tumours or cancers," Cucinotta said.

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.

"Current levels of radiation shielding would, at best, modestly decrease the exposure risks," Cucinotta said.

NASA plans to send humans to Mars in the 2030s.