Mars Mission Radiation Linked to Persistent Heart Scarring in Rat Study

A single exposure to simulated deep space radiation left rats with twice as much scarring around the heart’s small blood vessels 360 days later. The result raises a long-range health question for astronauts: could damage from a Mars mission emerge years after they return to Earth?

The study, published Sept. 30 in PLOS One, found signs of cardiac fibrosis, a buildup of scar tissue associated with a higher risk of heart failure. Because the experiment involved rats, it can’t establish that astronauts will develop the same condition. But the persistence of the changes makes long-term health monitoring a central concern.

“The message that we try to convey … is that the follow-up time is really important,” study co-author John Baker, a professor of surgery in the Radiation Bioscience Laboratory at the Medical College of Wisconsin, told Live Science. He said returning astronauts may live for decades after a mission, leaving time for cardiac disease to appear.

Separating radiation from weightlessness

Researchers used NASA’s Simulated Galactic Cosmic Ray Simulation (SimGCRSim), designed to more closely reproduce the radiation an astronaut could encounter during more than a year in deep space. The team exposed rats to a brief, size-adjusted dose intended to represent a round trip to Mars, estimated at roughly 18 months with current technology. Some animals also had their hind legs suspended to mimic weightlessness.

After 360 days, the irradiated rats had twice the scar tissue around small heart vessels as rats that weren’t exposed to radiation. Baker said the buildup can interfere with the heart’s ability to relax, potentially increasing the risk of heart failure.

Rats exposed to simulated weightlessness alone did not show the same heart scarring. That points to radiation as the cause of this particular change, Baker said. The weightlessness group did, however, have lower levels of key immune cells in later testing, a separate signal that microgravity may affect health over time. Research has already documented short-term effects of microgravity.

Radiation’s connection to heart problems is well documented, but direct evidence from long-duration exposure to galactic cosmic radiation remains limited. “No astronaut has ever been exposed to galactic cosmic radiation for long periods of time,” Baker said. His team’s earlier work had also identified cardiac changes in irradiated rats, while the new study used NASA’s simulator to model deep space exposure more precisely.

What the rat results can—and can’t—tell us

The researchers can’t directly translate the timing or severity of the rat findings to people. Humans typically live about 80 years, compared with roughly 2 to 4 years for rats. The authors suggest that changes appearing in rats after a year could take decades to become evident in humans.

Rupak Pathak, an associate professor of pharmaceutical science at the University of Arkansas for Medical Sciences with a doctorate in radiation biology, called the research “a very valuable contribution to space biology.” He told Live Science that rats and humans share more than 90% of their genetic information and have similar cardiac systems, while stressing that the species differ.

Pathak also pointed to a key limitation: the rats received radiation only once. He wants future studies to examine whether repeated exposure changes heart function or affects other vital organs. For Baker and his colleagues, that work could help NASA assess options such as heart medication or better spacecraft shielding before long missions begin. “The more we know before we start, then the better NASA is going to be at working out what types of countermeasures can be developed,” Baker said.

The practical takeaway is a research priority: track astronauts’ cardiovascular health well after deep space missions, while testing whether repeated exposure produces lasting effects that a single-dose rat study can’t capture.