Scott and Mark Kelly, identical twin brothers and astronauts for NASA are participating in a new study that is the first of its kind.  The study will look at the effects of long-term space missions on the human body, with the hopes of gaining insights on what will happen to humans on a mission to Mars.

For the study, Scott Kelly will travel with Russian cosmonaut Mikhail Kornienko to the International Space Station and stay there for a full year, the longest time any American has spent aboard the space station.  At that same time, Mark will return to his home in Arizona with his wife, former U.S. Representative Gabrielle Giffords over the same time period.

Throughout the year, blood, saliva, cheek swabs and stool samples will be taken from both the brothers at the same times before, during, and after the year long mission.  Psychological and physical tests will also be conducted at the same times as well.  NASA hopes to gain valuable insights on how long periods of time in space affect the human body.

"Our genes when the eggs split were exactly the same, and since then, the environment has changed them somewhat, but they're pretty much similar," Scott says.  "In any case, they want to look at what the space environment has done to my RNA, DNA, proteins, those kind of things in my body."

"The space environment is pretty severe,'' Mark says. "There's a lot of radiation involved that can affect your genes and your DNA and those things at the smallest level."

According to the brothers, who turned 50 last month, there were no initial plans to conduct this sort of experiment until it was mentioned by Scott, who asked if they planned to conduct this type of study.  Scientists at NASA considered the question asked by Scott and believed it had some merit.

The hope of NASA is that Scott's prolonged exposure to conditions in space could demonstrate some of the effects that astronauts on a mission to Mars could experience. 

"For me, having flown a long-duration flight before, on a personal level what makes it special is the duration, and the challenge that provides,'' Scott says. "From a scientific perspective, certainly the research about having a person spend longer than we've ever had an American spend in space is important because eventually we're going to go to Mars, leave lower Earth orbit, and we need to have that experience base of people living in space for much longer lengths of time.

"A flight to Mars and back could take three years, so the science value I think is pretty important. And also the science value of this particular study will allow us to learn things to help with those types of long-term missions."

Mark retired from NASA in 2011 after his wife, Giffords, was shot in the head in Tuscon, Arizona and has since made a remarkable recovery.

"For me, I don't work at NASA any more,'' Mark says. "I left after my wife was injured, so it allows me to still participate in some way. [Scott and I] never got to fly in space together, so this was some way [to participate together]." 

NASA has also stated that while onboard the ISS, the astronauts will perform more than a half dozen experiments to help researchers collect information on the psychological, biomedical, and medical challenges faced by humans under long term space flight.  According to NASA spokespersons, "these investigations will provide broader insight into the subtle effects and changes that may occur in spaceflight as compared to Earth by studying two individuals who have the same genetics, but are in different environments for one year."