Last year, NASA concluded an unprecedented study aimed at examining the effect of the microgravity environment of space. While the final results of the Twins Study — which, as the name suggests, involved the twin astronauts Mark and Scott Kelly — are yet to be announced, the preliminary results are already throwing up some unexpected findings.

According to an article published last week by Nature News, tests carried out before and after Scott’s yearlong sojourn on board the International Space Station (his brother Mark, a retired astronaut, stayed on Earth), have revealed changes in gene expression, DNA methylation — wherein methyl groups are added to DNA molecules — and several other biological markers.

However, it is still not clear which among these changes can be attributed to Scott’s time in orbit, and which were caused due to natural variations.

“The greatest importance of the study is to show that we can do it,” Andrew Feinberg, a geneticist at Johns Hopkins University School of Medicine in Baltimore, Maryland, and one of the researchers involved in the extensive studies, told Nature. “I don’t think people realized it would be so easy to do genomics on astronauts in space.”

Two of the key findings that have been revealed so far relate to the length of Scott’s telomeres — protective caps that cover the tip of chromosomes, and DNA methylation — a phenomenon that can affect gene expression. Surprisingly, the researchers found that when Scott returned to Earth, his telomeres were longer than Mark’s — exactly the opposite of what was expected. Moreover, during his year on the International Space Station, Scott’s DNA experienced less methylation than Mark’s.

Both these changes were reversible, and the measurements went back to pre-flight levels soon after Scott landed on Earth. Researchers are still trying to figure out why these changes occurred and what it means.

“Almost everyone is reporting that we see differences,” Christopher Mason, a geneticist at Weill Cornell Medicine in New York City, told Nature.

The earliest studies based on the treasure trove of data gathered as part of the Twins study may be published either later this year, or sometime in 2018.

The one-of-a-kind study afforded scientists a unique opportunity to understand how the hostile environment of space affects the human body — something that is key to successfully carrying out crewed deep space missions. The hope is that the data collected during Scott’s year in space will highlight some of the most worrying physiological and psychological hurdles to spending months or years in space — allowing scientists to find solutions to these problems before NASA attempts a flight to Mars and beyond by sometime around 2030.

“NASA is working on this science project that’s the greatest in the history of civilization,” Andrew Feinberg, director of the Center of Epigenetics at the Johns Hopkins Medical School, told the Washington Post last year. “They’re turning humankind from an Earth-dwelling species into a space-exploring species. One day, humankind will be a species that can settle on other planets. It might be a hundred years before we have humans living on Mars, but this is a whole new kind of science. It’s a multi-generational effort.”