Getting a manned mission safely to Mars would be the greatest space-age accomplishment of all time. Humans have never visited another planet, and while we’ve traveled to the Moon and back the challenges a Mars mission creates are obviously on an entirely different level.

NASA and other organizations around the world are already working hard to solve problems posed by a trip to Mars, but a new study published in the Proceedings of the National Academy of Sciences suggests we’ll need to look within ourselves before we decide to head to the Red Planet.

In the paper, researchers from Georgetown University Medical Center explain how radiation from space affects gastrointestinal tissue and issue a stark warning to anyone planning on sending humans on long-haul space missions.

The study focuses on the effects of heavy ions interacting with living tissue, highlighting the effects the particles have on the stomach and colon, which are particularly vulnerable to disruption. Earth’s magnetic field does a good job of protecting us against the bombardment of radiation from space, but travelers headed to Mars or beyond wouldn’t be so fortunate.

Unfortunately for astronauts, nobody has come up with a suitable solution for protecting them against this kind of cosmic radiation, and it would absolutely need to be addressed before any space agency decides to send manned missions to the Red Planet. The team’s work shows that disruptions in the tissue that are caused by space radiation can hinder the function of the gastrointestinal system and dramatically increase the risk of tumor development.

“With the current shielding technology, it is difficult to protect astronauts from the adverse effects of heavy ion radiation,” Kamal Datta, a co-author of the study, explains. “Although there may be a way to use medicines to counter these effects, no such agent has been developed yet. While short trips, like the times astronauts traveled to the Moon, may not expose them to this level of damage, the real concern is lasting injury from a long trip, such as a Mars or other deep space missions which would be much longer.”

The safety of the first Mars travelers (and all subsequent missions, of course) is of utmost importance. The immense amount of time and investment that will go into the first manned trips to Mars mean that keeping the astronauts in top physical condition is a top priority. Nobody wants to do their job with tumors growing in their gut, so developing a protective mechanism to keep the crew safe should be top of NASA’s to-do list.