Scientists may have underestimated the effect of cosmic rays on humans as they leave Earth’s atmosphere and are exposed to the deadly radiation.

NASA is dead-set on sending astronauts to Mars within the next 15 to 20 years. China has said it hopes to send people there between 2020 and 2030, and even Russia is floating plans to put boots on the red planet.

The first colonists on Mars will be tasked with flying a massive spacecraft to the planet, landing safely, laying the groundwork for a future civilization, conducting vital scientific research, and getting back to Earth. But, lurking between those stressors will be something much more cynical: radiation.

It’s been said that the first Mars explorers will have to be prepared to take one for humanity. As various studies have shown, they risk permanent neural damage as well as an increased risk of leukemia and Alzheimer’s disease. And now, scientists at the University of Nevada, Las Vegas have added to this list with a new study that shows how a deep-space mission to Mars could double astronauts’ risk of getting cancer.

New research from scientists at the University of Nevada, Las Vegas (UNLV) shows that the cancer risk for astronauts undertaking long-term missions to Mars or any other destination beyond Earth’s magnetic field is actually twice what we previously thought.

You might want to hold off on purchasing a ticket to Mars. The risk of developing cancer from the galactic cosmic rays on Mars is twice as high as originally estimated, according to a new study published in Scientific Reports.

Practically everyone who likes space and has lots of money is trying to get to Mars in the near future. But before anyone reaches the Red Planet, there are plenty of concerns to mull over, most notably that our bodies were not built to live in a barren litter box with a thin atmosphere. But the journey to Mars is an equal concern. An unnerving new study suggests that the trip to Mars could put passengers at a higher risk to develop cancer—possibly two times greater than what experts previously thought.

Everyone is well aware that sending humans to Mars means overcoming a number of major problems, one of which is the cancer risk for the astronauts. But it seems that even NASA's best risk projections were way off the mark. The latest research suggests the cancer risk is actually double what we thought.