Newly elected Arizona Sen. Mark Kelly and his twin brother took part in a groundbreaking NASA experiment for 4 years. Here's what we learned from it.

Newly elected US Sen. Mark Kelly and his brother Scott Kelly participated in a groundbreaking four-year NASA study to uncover the long-term effects of space on the human body. Over nearly a year, the twins took the same medical tests — one while aboard the International Space Station and the other while back on Earth. The results, published in the journal Science, revealed that a year in space has considerable but not-life-threatening effects on the human body, offering hope that a longer-term journey to Mars is possible.