Rendezvous with a Rock
MESSENGER spacecraft is approaching it's rendezvous with Mercury. After flying for over 2400 days, in a little over 24 hours (from writing this) MESSENGER will maneuver into orbit, the first time a satellite has orbited Mercury. We hope to learn a lot about the composition of the surface and effects of solar weathering of the surface. And there's the prospect of photographing the sun-side of the planet for the fist time!
In a few months, Dawn spacecraft will orbit Asteroid Vesta – the first time we've orbited an asteroid. We hope to learn more about the composition of asteroids. (We've landed on one, but technically it's harder to orbit than to land. We've also successfully landed on a comet with Deep Imact…) Dawn has not been in flight as long as MESSENGER, but it's orbital attempt is none the less impressive (Vesta is much smaller than Mercury).