Effects of astronaut's yearlong space trip on body to be studied, could lead to future Mars mission

America's all-time space endurance champion is finally back on Earth. Astronaut Scott Kelly just completed a 340-day mission aboard the International Space Station and scientists hope the mission will help pave the way to Mars.

Kelly will undergo some of the most in-depth medical testing to see how his body changed during all that time in space.

"We are talking about muscle strength, muscle coordination, blood, urine analysis, EKG, heart and lung performance, pulmonary capacity … the bone density scan - all of this compared to his pre-flight," said retired NASA astronaut Tom Jones.

Jones and his crew actually set up the research lab in the space station 15 years ago. It is the lab Kelly used during his space trip.

Perhaps the best gift of all to scientists is Kelly's identical twin - astronaut Mark Kelly. He has been on Earth the entire time.

It is the greatest scientific measurement researchers could ask for. It will allow them to identify any genetic changes that may have happened to Scott Kelly in space.

"In a very material way, he has been having to work out two hours every day to try to maintain his health while being productive just like an astronaut would have to on the way to Mars," said Jones. "So this is an early footstep, an early milestone on the way to Mars."

Jones said NASA can start looking at outposts near the Moon where they could perhaps send someone for six to ten months to see how the body reacts.

Meanwhile, Scott Kelly will have to re-acclimate before the months of medical testing begin.