Well, why don't you go see what Phil Plait, the coolest and most engaging science blogger I've come across, has to say about the deceptively simple image:
I simply can't compete with Phil's description, so I'll leave you with his words:
Think on this, and think on it carefully: you are seeing a manmade object falling gracefully and with intent to the surface of an alien world, as seen by another manmade object already circling that world, both of them acting robotically, and both of them hundreds of million of kilometers away.
Never, ever forget: we did this. This is what we can do.