If your heart stops en route to Mars, rest assured that researchers have considered how to carry out CPR in space. (One option is to plant your feet on the ceiling and extend your arms downwards to compress the patient’s chest.) Astronauts, because of their age range and high physical fitness, are unlikely to suffer a stroke or have their appendix suddenly explode. That’s good because, if it does happen, they’re in the realm of what Scott describes as ‘treatment futility’. In other words: there’s nothing anyone can do about it. On the ISS, when medical incidents arise, astronauts can draw on the combined expertise of a host of medical experts at Nasa. “The patient is on the space station, the doctor is on the ground, and if there's a problem the patient consults the doctor,” says Scott. By the time astronauts reach Mars, there’ll be a 40-minute time lag in communications, if it’s possible to make contact at all. “We have to begin preparing for not only being able to diagnose things in spaceflight but also to treat them as well,” Scott says. Artificial intelligence is likely to be a part of the solution. If you’re imagining the holographic doctor from Star Trek, downgrade your expectations, at least for the next few decades. Kris Lehnhardt, the element scientist for exploration medical capability at Nasa, says: “We are many, many, many years away from: please state the nature of the medical emergency.”