Scott Kelly, who has been in space for nearly a year, has finally come back to Earth. The long-anticipated study, The Twins Study, is now complete. Researchers will be comparing data from Scott Kelly to that of his twin brother Mark Kelly, a retired astronaut. Overall, ten groups of researchers will be studying a variety of information related to Kelly and his brother, ranging from overall health, immune response, bone formation, gut microbiome and DNA.

On a genomic level, scientists have discovered a supposed “space gene” that has been activated in Kelly’s body. By comparing and contrasting the genome sequences in the white blood cells of the two brothers, the siblings have hundreds of unique mutations—with more than 200,000 RNA molecules presented differently. Chemical modifications in Kelly’s DNA were present, though these quickly reverted once he was on Earth, leading scientists to hypothesize that genes are sensitive to environment change. In terms of bone formation, Kelly experienced declining bone formation, but a healing hormone that helps with bone and health increased significantly, most likely caused by the intense exercise Kelly was put through to combat declining bone formation.

On a mission to Mars, an astronaut’s first actions on the surface could be crucial. Based on Kelly’s experience in space, many scientists think that the task may be more difficult than first imagined. For instance, Kelly was given difficult tasks in space, such as performing daily movements to test muscle dexterity, various sitting positions to test postural control, and to test functional motor skills, the Functional Task Test. Kelly was subject to climbing ladders, opening hatch doors, jumping down, and using tools among other things. Surprisingly, scientists have discovered that the Kelly’s fine motor skills have held up well in a zero gravity environment when compared to a space-time flight of six months. It also seems that the adjustment to sleep in space over a longer period of time has improved. Kelly was recorded to have seven hours of sleep, compared to astronauts who have been in space for only six months, who only had six.

In short, NASA Human Research Program chief scientist John Charles remarked that the “preliminary results are reassuring that a year in space is not significantly more stressful than six months in space. However, more definitive insights must await the further analysis of the samples and supporting data, the correlation of findings among all the investigators, and future long-duration ISS missions with these and other genetic investigations.”