For 340 days, Scott Kelly calls the land aboard the International Space Station and collects data about himself.
He took blood from his arms. He saved his urine. He played computer games to test his memory and reaction rate. He measured the shape of his eyes.
Two hundred and thirty miles below, mr. Scott's twin brother Mark, who also served as an astronaut, performed identical tests. Now, a comparison of these two men has given a unique opportunity to learn what happens to the human body in space – down to molecular level.
The researchers found out that Mr. Kelly's body experienced a large number of changes in circulation. DNA mutated in some of his cells. His immune system produced a large number of new signals. His microbiome was given new bacterial species.
Many of these biological changes seemed harmless and disappeared after he returned to earth . But others – including genetic mutations and after the return fall into cognitive test results – did not correct themselves and provoked concern among researchers.
Some considered the risk that could be handled while others wondered if it would be safe for astronauts to travel long distances to Mars or beyond. The final answer will depend on studies of more and more astronauts.
"I think it's the most comprehensive assessment of people to date," says Dr. Eric Topol, director of the Scripps Research Translational Institute, who was not involved in the study. "I don't know there has been anything close to this."
Although astronauts have been carried high for almost six decades, there is a lot of life in space that scientists still do not understand. NASA wants to solve some of the mystery before sending astronauts on longer planes.
In 2012, NASA chose Mr. Kelly to attend Russian cosmonaut Mikhail Kornienko aboard the space station for an annual study of the challenges of space travel, twice as long as previous studies.
In the wake of the mission statement, Mr. Kelly officials if they had plans to compare him with his twin. "We have these two guys who are genetically identical," Mr. Kelly recalled telling them. "They wanted to make an interesting experiment."
Officials had no such plans, but soon decided to pick him up on the offer. Mark Kelly agreed and the NASA Twins Study was born. (Mark Kelly, retired from NASA in 2011 and man of former representative Gabrielle Giffords, driving for John McCain's Arizona Senate seat.)
By comparing the brothers, NASA hoped to better understand the changes that Scott Kelly experienced during his mission.
"That they are twins really narrows the alternatives," said Susan Bailey, a cancer biologist at Colorado State University and co-author of the new study. "We can say that we can tell that these changes are due to spaceflight."
Ten research teams prepared experiments for the twins; They will probably bring an avalanche of research. But to Mr Kelly, experience did not feel much different from previous missions.
Drawing his own blood in zero gravity was a well-known routine. "I've had a few wastes in my time," Kelly said. "You stretch yourself straight out and take the blood of blood."
In many measures, the researchers eventually found that Kelly changed as much as astronauts who remained at the space station for only six months. Eventually the pace of biological change slowed, suggesting that the human body might reach a new balance in space.
But Mr. Kelly's body was also changed in some surprising ways.
Dr. Bailey studied special sections of his DNA called telomeres, which are at the end of chromosomes, protecting them from deterioration.
As people grow old, their telomeres tend to be shorter. Stress – such as. Radiation or pollution – can accelerate aging by breaking telomeres even faster than normal.
Oddly, the average length of Mr. Kelly's telomeres in the room instead of falling as if his cells became more youthful.
Regular exercise and a healthy diet can be part of the cause. But going to the room may also have awakened a quiet population of stem cells in Mr. Kelly's body, Dr. Bailey.
His cells may not have grown longer telomeres, in other words. Instead, his body produced a new supply of young cells with longer telomeres.
Going to the room also seemed to trigger a genetic shift in Mr. Kelly. Thousands of genes that were once silent increased their activity – genes that remained silent in Mark Kelly's body back on earth. The longer Scott Kelly remained, the greater the number of genes becoming active.
Some of the awakened genes are known to encode proteins that help repair damaged DNA. It would make sense as the radiation levels in the international space station are higher than on the ground.
Christopher Mason, a geneticist at Weill Cornell Medicine in New York, estimated that Mr. Kelly was exposed to 48 times more radiation than the average ground exposure over a year. His cells could have been busy repairing radiation damage.
However, a number of other activated genes play roles in the immune system. What exactly triggers these changes is not clear.
It may be the general stress of life in the space station evoking an immune response. But recent studies have also shown that latent viruses can awaken in astronauts.
Or maybe it's that the immune system, which never evolved to survive in space, just gets confused.
"Is it good or bad? We just know it's more," said Dr. Mason, co-author of the new study, on immune activity. "To know that, we would need more astronauts."
Mr. Kelly's return to earth on March 1, 2016 proved to be one of the greatest moments – biologically – of the entire mission. His body showed signs of intense stress, and his immune system was in high gear.
Michael Snyder, a geneticist at Stanford University and co-author of the research, warned that this response might not be typical. "Maybe he got a virus infection," he wondered. "That's why you want to see it in more people."
Despite that shock, Kelly's body traveled mostly back to preflight mode. For example, some species of bacteria thriving in his intestine while in the room were rarely on his landing.
The strange extension of Mr. Kelly's telomeres disappeared after less than 48 hours on Earth. In fact, Dr. Bailey and her colleagues find many cells with telomeres that were shorter than before Mr. Kelly went to the room.
"People have asked me," Well, will it accommodate the youth fountain? "Dr. Bailey said," I don't think so. If it is, you must stay up there forever. "
" Fighting through quicksand "
Some aspects of Mr. Kelly's biology did not go back to the preflight norm.
Six months after he returned to earth, 8, 7 percent of his genes were still in a changed way, small-scale judges of this shift described Dr. Snyder's change as the message
The researchers also found that Mr. Kelly did not do well when he came on cognitive exams "He became slower and less precise on almost all the tests," said Dr. Mathias Basner, a cognitive researcher at the University of Pennsylvania.
It is possible that some biological changes were due, but Dr. Basner noted that Mr. Kelly also faced many demands back on Earth, including a busy schedule of television interviews and public speaking.
And at an unconscious level, he can no longer push himself. "I mean, he read back in essence the moment he hit the ground, and so must he was just not so motivated anymore, "said Dr. Basner.
In his 2017 memoir, "Endurance," Mr. Kelly describes fighting for his return with pain, sleeping problems and other ears. One night he felt as if he "fought through mercury", he wrote.
Last week, in an interview Kelly asked that these difficulties could be due to his cognitive scores. "It's hard to concentrate when you're not comfortable," he said.
Another lasting change found by researchers was a collection of genetic mutations that Mr. Kelly got in the room. "We see them appearing in flight, and they then continued," said Dr. Mason.
Radiation sometimes triggers a type of mutation which makes cells prone to gain more and more mutations as they share. Eventually, the cells can begin to grow uncontrollably – "take steps towards cancer," says Dr. Bailey.
Peter Campbell, a cancer biologist at the Wellcome Sanger Institute in the UK who was not involved in the new study, said Scientists cannot predict what the extra mutations will mean to Mr. Kelly's Health.
"It's hard to be sure, but I think those kinds of numbers will be associated with a moderate increase in cancer risk," he said.
These two long-lasting changes – in Mr. Kelly's cognition and DNA – left a number of experts concerned about the risk of a trip to Mars that could take a year.
Gary Strangman, a psychologist at Harvard Medical School, said a fall in speed and accuracy could potentially have serious consequences for long-term missions. "
After a dizzying journey to the Red Planet, the astronauts would probably have to take quick and accurate action when they landed.
" If you had a period of slower cognitive rate and difficulty with balance and eye-head coordination, these behaviors would be in danger, "says Rachael Seidler, a cognitive neuroscientist at the University of Florida.
A heavy load of genetic mutations would not present immediate dangers to astronauts on the mission but it could increase their lifelong risk of cancer.  Dr. Mason estimated that a mission to Mars would expose an astronaut to eight times more radiation than Mr. Kelly experienced.
"All efforts must be made to limit exposure to astronauts during periods of prolonged space travel," said Charles Swanton , a cancer biologist at the Francis Crick Institute in the UK, who was not involved in the new study.
Dr. Topol, from the Scripps Institute, found the consequences of Mr. Kelly's experience to be grim.
"The main conclusion I got from this paper, based on all the objective data, is why would anyone like to go to Mars or be in space?" He said. "Because this is really scary."
Jerry Shay, a cell biologist at the University of Texas Southwestern Medical Center, was much more optimistic. He was hoping for countermeasures that would protect astronauts.
Already, he and his colleagues already tested drugs to trigger cells to repair DNA damaged by radiation. "I think all these problems are soluble," said Dr. Shay.
NASA has begun to sail through all these achievements to help plan the next mission round to the International Space Station.
"It won't be a replication of what you saw in the Twins Study," says Jennifer Fogarty, chief scientist at NASA's Human Research Program.
"We must learn from it and we become more intelligent about the questions we ask. There are many fascinating things to do. It's just not clear what that means."
Dr. Bailey, for his part, plans to continue studying Mr. Kelly's enchanting telomeres. Solving this mystery can shed light on ordinary aging and the diseases it brings.
"When we figure out how and why, it will be important for astronauts as well as for us just breeders," she said. 19659068]