Before you ask: yes, the researchers are aware that the study is only covering a handful of people. It may take many more astronauts to reach a definitive conclusion. However, the outcome parallels what the team saw when subjecting mice to the same levels of radiation you'd get on a trip to the Moon. The irradiated rodents were disproportionately likely to suffer heart problems as they aged, just on a much shorter time scale.

This doesn't mean that humans will have to stay near Earth to avoid a premature death. The findings challenge the all-clear message from earlier studies, though, and may give space agencies a reason for pause as they prepare for human travel to Mars. Spacecraft and spacesuits may need extra protection to ensure that crews lead long, healthy lives.