Before he passed away Sagan recorded a message to future explorers of the cosmos, solar system, and Earth. Here is a snippet that went around the internet the other day after NASA successfully landed the rover Curiosity:
maybe we're on Mars because of the magnificent science that can be done there - the gates of the wonder world are opening in our time. Maybe we're on Mars because we have to be, because there's a deep nomadic impulse built into us by the evolutionary process, we come after all, from hunter gatherers, and for 99.9% of our tenure on Earth we've been wanderers. And, the next place to wander to, is Mars. But whatever the reason you're on Mars is, I'm glad you're there. And I wish I was with you.
Sagan, we wish you were with us.