Astronaut Scott Kelly, the twin brother of Tucsonan and retired astronaut Mark Kelly, is headed back to earth tonight from nearly a year in space aboard the International Space Station. 

Apollo 13 Commander James Lovell talks about why Kelly's long trip was important:

Given these risks, why fly in space for a year?

Again, I must recall the words of President Kennedy: We pursue these ambitious goals of space flight “not because they are easy, but because they are hard.”

There is another reason: discovery. Scott has flown so long so we can make huge advancements in our understanding of how long-duration space flight impacts human physiology, something that is essential if we are ever going to travel to more distant destinations, such as Mars.

And because Scott happens to have an identical twin brother — a fellow retired astronaut and my friend, Capt. Mark Kelly — NASA researchers are using Mark as a control subject on Earth while Scott serves as the test subject 250 miles above us to gain even more knowledge about how living in a zero-gravity environment changes us.

One day, an American will walk on Mars. But we will get there only because we chose to do it and because our leaders in Washington decided it was important.

These future missions will show and Scott’s flight has demonstrated the power of American purpose: one person facing the mortal dangers of space for the sake of international cooperation, science and exploration; the resolve to once again test the limits of risk in order to win progress; and a nation marshaling its innovation to realize that victory.

The New York Times rounds up some fun facts about Kelly's trip here.

Meanwhile, National Geographic rounds up 15 of the best photos that Kelly posted on Twitter here.