One of the twins will be sent to live on board the International Space Station, while the other remains on Earth. Scott Kelly will spend a year on the ISS, which will break the current NASA record for continuous time spent on board, while his brother Mark will act as a control in the experiment, according to Sky News.

NASA To Use Identical Twins In Space Experiment

NASA studying effects of space on our bodies

Scott Kelly spoke about the NASA experiment back in January, and claimed that it “is really going to help us learn a lot about the negative effects of space on our human physiology and then hopefully we’ll figure out how to mitigate that.” His brother Mark, husband of former U.S. Congresswoman Gabby Giffords, will play a crucial role as a control factor.

The head of NASA’s Human Research Program, Dr John Charles, said that scientists will compare the two astronauts to find out what effects space travel has. “It’s a way to start using 21st century medical technology to understand what happens to people in long-duration space flight,” he said.

Scott is expected to perform various experiments and undergo medical tests during his time in space, and it is hoped that the experiment will inform scientists on how to prepare NASA astronauts for a future manned mission to Mars.

Monitoring genetic changes

It is thought that Scott will return slightly taller than Mark due to the lack of gravity in space, something which he seems to be looking forward to. “This time hopefully it will last long enough so that when I get back to the US I can look down at him a little bit,” Scott said in jest.

The 50-year-old twins share almost identical DNA, and NASA scientists want to find out whether the highly radioactive and weightless environment of space will leave Scott with noticeable genetic differences upon his return.

“The environment that Scott is going in is pretty unforgiving, a lot of radiation, no gravity and lots of opportunities for genetic material to change and for genes to mutate,” said Mark.

The mission will launch from Kazakhstan on March 27. Scott will be joined by Russian cosmonaut Mikhail Kornienko, who will also stay for a year.