Astronaut Scott Kelly's DNA Is No Longer the Same as Identical Twin Brother After Year in Space

The year-long mission was the first of its kind.

Astronaut Scott Kelly, who spent a year in space, now has different DNA than his identical twin brother, according to a new study conducted by NASA.

Preliminary findings indicate that Scott Kelly has a seven percent difference in genetic makeup than his brother Mark Kelly after 340 days aboard the International Space Station.

Most of the biological changes Scott experienced in space quickly returned to nearly his pre-flight status, some within hours or days of landing on March 1, 2016, while a few persisted after six months, according to the study.

But, the remaining seven percent of the genetic changes point to possible longer term changes in genes related to his immune system, DNA repair, bone formation networks, hypoxia (or oxygen deficiency) and hypercapnia (excessive carbon dioxide in the blood).

"The Twins Study has benefited NASA by providing the first application of genomics to evaluate potential risks to the human body in space," according to a statement from the space agency.

Another interesting find was that Scott’s telomeres (endcaps of chromosomes that shorten as one ages) actually became significantly longer in space, but shortened two days after his return.

Scott Kelly’s mission was twice as long as an astronaut's term aboard the International Space Station.

It is reportedly a "stepping stone" to an eventual three-year mission to Mars, NASA said.