The Twin Study, seen as the ultimate test of nurture versus nature, "may prove useful in the development of new treatments and preventive measures for related health issues on Earth", according to NASA. While Scott spent a year in space for the experiment, Mark remained on Earth as the control subject.
Of particular interest were the changes to Scott's DNA.
After spending a year in space, NASA astronaut Scott Kelly is not the man he used to be - at least genetically speaking. Scott, on the other hand, spent nearly a year orbiting the Earth on a mission that started in March 2015.
"The ideal nature versus nurture study was born", NASA officials said in a statement. If scientists are hoping to successfully launch a three-year mission to Mars, understanding how being in space affects one's DNA (for the better or worse) is no doubt an integral one.
As part of NASA's goal to send astronauts on long-duration space flights to Mars and beyond, this record-setting stay in space was created to test the limit of human endurance in a microgravity environment. As it turns out, this isn't too far from the truth. Countermeasures are being investigated. Scientists discovered Scott's telomeres - the endcaps of chromosomes that shorten as you age - actually grew longer during his one year in space. However, most of the telomeres returned to normal lengths within two days of Scott's return to Earth.
NASA clarifies in the report 93 percent of Scott Kelly's genes returned to normal after he came home, but that the missing 7 percent points "to possible longer-term changes in genes related to his immune system, DNA fix, bone formation networks, hypoxia, and hypercapnia".
While 93 percent of his genetic expression has returned to normal, several hundred "space genes" have remained altered, the data suggests. Scott's voyage is now the longest documented space mission completed by an astronaut, and is a stepping stone to a three-year mission to Mars.
However, a more pronounced decrease in speed and accuracy was reported postflight, possibly due to re-exposure and adjustment to Earth's gravity, and the busy schedule that enveloped Scott after his mission, the agency said.
"All of these findings are being integrated and summarized by the research teams; researchers are also evaluating the possible impact that these findings will have on future space travel beyond low Earth orbit", NASA officials said.