USA Today

July 20, 1969: What a day for America—and the world. With one step on a powdery chunk of lunar surface, we achieved the unachievable: Apollo 11 landed on the moon. Few events have had the same impact on our times, according to these five distinguished Americans.

Mars. Rogue asteroids. It's exciting stuff. And this time around, it's not just NASA. Here are four trips to keep your eye on.