In 1971, a red-headed, tree-loving astronaut named Stu ‘Smokey’ Roosa was asked to take something to the moon with him. Of all things, he chose to take a canister of 500 tree seeds. After orbiting the moon 34 times, the seeds made it back to Earth. NASA decided to plant the seeds all across the country and then… everyone forgot about them. Until one day, a third grader from Indiana stumbled on a tree with a strange plaque: "Moon Tree." This discovery set off a cascading search for all the trees that visited the moon across the United States. Science writer, and our ve...