Roamy here. Early this morning, the Dawn spacecraft entered orbit around the asteroid Vesta.
It will remain there for a year then move to orbit around the dwarf planet Ceres. (I am not getting into the whole dwarf-planet / proto-planet / what-do-we-call-Pluto-now argument.)
The Dawn spacecraft uses ion propulsion, similar to the engines used on Deep Space 1. Deep Space 1 had a similar mission, rendezvousing with the asteroid Braille and Comet Borrelly. Ion thrusters have higher specific impulse but less thrust. You can’t launch a satellite with an ion thruster, but there’s a lot of weight savings for missions like this. Ion thrusters have also been used for satellite stationkeeping.