Investigation on impact of life in space on human body could inform potential missions to Mars

When Nasa set out to study identical twin astronauts – one orbiting in space for nearly a year, the other left behind on Earth – the outcome was uncertain. Would Scott Kelly return to Earth younger than his brother, Mark, as depicted in the film Interstellar?

The answer, outlined in the most comprehensive investigation on the impact of life in space on the human body, is that there were apparently no substantial or lasting health changes. However, the findings reveal subtle biological effects caused by Scott’s 11-month residence in zero gravity at the International Space Station. Scientists say these could provide crucial information about the risks posed by future long distance missions to Mars and beyond.

“This opens a door to the kind of analysis you could never do before, that’s going to be important for astronauts when they go on long duration space flight to Mars and they’re going to have be progressively independent from the resources that are on the ground,” said Andrew Feinberg, a professor of medicine at the Johns Hopkins University and co-author of the study.

Scott Kelly: ‘I came back from space younger than my twin’ Read more

Scientists have long monitored the physiological effects of space travel on astronauts. However, most of these astronauts travel on missions of six months or less, and no previous studies have involved a genetically identical control back on Earth.

Ten teams of investigators were recruited to monitor and analyse almost every aspect of the Kelly twins’ physiology, from gut bacteria to gene activity and cognitive abilities, before, during and after Scott’s 2015-16 stay at the ISS.

Changes included striking differences in gene activity in Scott. Some of these genes related to the immune system, which is under greater strain in space.

Other differences included to the shape of Scott’s eyeball, including a thickened retinal nerve, while the skin on his forehead became thicker. These effects are thought to be because more fluid gathers in the head without the usual downwards pull of gravity. A series of tests also showed Scott’s cognitive abilities declined slightly.

Perhaps most intriguing was what happened to the astronaut’s telomeres – tiny structures that sit at the ends of chromosomes, like the plastic ends of shoelaces. The length of telomeres gives an indication of ageing – they shorten throughout life and in particular during times of physical stress.

Isolation and hallucinations: the mental health challenges faced by astronauts Read more

Scott’s telomeres unexpectedly lengthened in space, contrary to what might have been expected. Susan Bailey, professor at Colorado State University, who led this element of the research said: “We’re scratching our heads on exactly how those really dramatic shifts in telomere length are happening. I don’t think that that can really be viewed as the fountain of youth and that people might expect to live longer because they’re in space.”

After returning to Earth, Scott’s telomeres shortened again, bringing him back in line with his brother.

Mike Snyder, a geneticist at Stanford University, said: “There are thousands of genes and molecular changes that occur as someone goes in space. Somewhat reassuring of course, is that when he comes back … virtually all of those returned to normal by six months.”

The scientists had to contend with a variety of challenges, including being able to collect enough blood from Scott (blood volume shrinks during space flight due to dehydration. One shipment of equipment blew up aboard a SpaceX rocket. And they also faced other scientific limitations: while genetically identical, the twins had different lifestyles in space and on Earth.

Mark was able to drink alcohol, while Scott was forbidden from doing so, for instance. “Even the tiniest little whiff of alcohol actually does something to the electronic components that I think Nasa doesn’t totally understand, but they ban all alcohol,” said Feinberg. “And that can have a significant effect on the epigenome.”

The findings are published in the journal Science.