Who Is Scott Kelly's Twin, Mark Kelly? Get To Know The Other Half Of NASA's Twin Experiment

On Friday, NASA astronaut Scott Kelly launched into space for a year-long mission at the International Space Station (ISS), along with Russian cosmonaut Mikhail Kornienko. When Kelly returns to Earth in 2016 he'll have set a U.S. record for the most time spent in space, racking up 522 days throughout his career. Along with his work for NASA, Kelly will participate in a study testing how the human body reacts to long periods of time in space, in which his body will be compared to his twin brother's, who will stay on Earth. So, who is astronaut Kelly's twin brother?

Apparently an infatuation with space runs in the family, because Scott's twin, Mark, is a retired astronaut, as well as a Navy Captain. As a naval pilot, Mark, now 51, flew combat missions in the Gulf War and became a NASA space shuttle pilot in 1996. He flew his first mission into space in 2001, delivering supplies and a new crew to ISS. During his nearly 12 days in space, Mark orbited the Earth 186 times and travelled more than 4.8 million miles. Mark went into space for the second time in 2006 for nearly 13 days in order to test new safety techniques after the Columbia STS-107 aircraft, along with its seven crew members, was lost in 2003.

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Mark returned to ISS two more times, in 2008 and 2011, spending 14 days and 16 days in space respectively, before retiring from NASA later in 2011. His final mission aboard Space Shuttle Endeavour was also the Endeavour's last mission. Adding to numerous awards from the Navy, Mark was awarded the NASA Exceptional Service Medal and a NASA Space Flight Medal with three bronze service stars for his work as an American astronaut.

Mark is married to Gabby Giffords, the former Arizona congresswoman who was the victim of an assassination attempt in 2011. Giffords was shot in the head during a meeting with her constituents in Tucson and recovered after emergency surgery and extensive rehab. She resigned from Congress in 2012 to focus on her recovery and the husband and wife duo later wrote a book together about Giffords' recovery titled Gabby: A Story of Courage and Hope. The two now advocate for gun control and started the political action committee Americans for Responsible Solutions.

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Since Mark will remain on Earth while his brother floats around in space for a year, scientists will collect and analyze genetic, molecular, and physiological data from the identical twins in order to study how spending long periods of time in space affects the body. The main focus of the research will be the men's eyesight because scientists remain puzzled as to why U.S. astronauts often experience some loss of vision after spaceflight. Having identical twins to study makes for the ideal experiment, as no two humans could be more similar.

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