A new NASA study reveals how an astronaut鈥檚 eyeball shape changed and his cognitive ability declined during a year-long space mission by comparing him to his Earth-based identical twin.
Scott Kelly, 51, spent nearly a year in orbit on the International Space Station on a mission that ended in March 2016, while his identical twin Mark, a former astronaut, remained on Earth as a control subject.
鈥淭he selection of a pair of identical twin astronauts for NASA鈥檚 first one-year mission enabled us to compare the impact of the space flight environment on one twin to the simultaneous impact of the Earth environment on a genetically matched subject,鈥� the report鈥檚 authors said.
Scientists identified thousands of molecular changes in Scott compared to his brother, some of which persisted after his time in orbit.
His eyeball shape changed, including a thicker retinal nerve, and there was a small change to Scott鈥檚 DNA and genes, especially related to the immune system.
The study also found that Scott鈥檚 telomeres, found at the end of chromosomes and related to aging, lengthened during the space flight.
This chromosome inversion was still found nine months after he returned to Earth, but eventually stabilized to near pre-flight averages.
鈥淭he potential importance of such shifts in telomere length (elongation and accelerated shortening or loss) is underscored by accumulating evidence that supports telomere length not only as a robust biomarker of aging but also as a determinant of age-related diseases, such as cardiovascular disease and cancer,鈥� the authors wrote.
鈥淏ecause such metrics can inform overall health, monitoring telomere length dynamics represents an important element of evaluating health and potential long-term risk for future astronauts.鈥�
Ninety per cent of Scott鈥檚 genes returned to normal after the flight, the study鈥檚 authors said.
鈥淚t is unknown if any of the changes that persisted in Scott upon return to Earth are related to space flight alone or how long they will last,鈥� the American Association for the Advancement of Science said in a press release.
The study found no significant health differences for Scott, but the results were useful to see the effect on astronauts who are in space longer than six months, the AAAS added.
鈥淭he persistence of the molecular changes and the extrapolation of the identified risk factors for longer missions, greater than a year, remain estimates and should be demonstrated with these measures in future astronauts,鈥� the study鈥檚 authors concluded.
鈥淐hanges described in this study highlight pathways and mechanisms that may be vulnerable to space flight and may require safeguards for longer space missions; thus, they serve as a guide for targeted countermeasures or monitoring during future missions.鈥�
The future of long-term space travel
Academic Francine Garrett-Bakelman and colleagues from various U.S. universities used a range of measures to evaluate the Kelly brothers before, during and after Scott鈥檚 year-long mission.
鈥淢easurement of the same variables in an astronaut on a year-long mission and in his Earth-bound twin indicated the biological measures that might be used to determine the effects of spaceflight,鈥� the study鈥檚 authors wrote.
鈥淕iven that the majority of the biological and human health variables remained stable, or returned to baseline, after a 340-day space mission, these data suggest that human health can be mostly sustained over this duration of space flight.鈥�
Biological samples were collected from Scott while he was aboard the ISS and returned to Earth in Soyuz resupply rockets.
The twin study was Scott鈥檚 idea, according to Andrew Feinberg, a professor at John Hopkins University Schools of Medicine, who was part of the team that wrote the study.
鈥淪cott and Mark both have the same DNA sequence, in other words the letters of the alphabet,鈥� Feinberg said.
鈥淏ut because they are two different people who have had two different life experiences, including these differences in flying in space, then there are other marks on the DNA, called epigenetic information, that could be different between the two twins.鈥�
The study鈥檚 findings will be beneficial to longer space missions, such as trips to the Red Planet.
鈥淭he real question is can we use this kind of information to predict what鈥檚 going to happen to people when they go on long distance missions to Mars,鈥� Feinberg added.
He suggested the next step should be to look at space missions of varying length and apply the methods developed in the study to project likely biological changes in astronauts on multi-year missions.
鈥淚f we could do that we might be able to anticipate in astronauts, individually or as a group what sort of health problems they might run into,鈥� he said.
鈥淲e won鈥檛 have the problem of a single set of observations then, we鈥檇 have a much larger number.鈥�
鈥淭he NASA Twins Study: A multi-dimensional analysis of a year-long human space flight鈥� was published Wednesday.
