Today's APOD (Astronomy picture of the day) is of Vesta, a rocky asteroid named after the Roman goddess of home and hearth. Vesta is the second most massive asteroid in our solar system, but the first to be visited by the Dawn spacecraft which finally arrived there in July after launch in 2007 under power of its three xenon ion thrusters. Yes, I said Ion Thrusters.

Star Trek fans will recognize this as "ion drive" and won't confuse it with ion propulsion a more highly advanced technology not developed until sometime after 2268. NASA was clearly not aware of this semantic difference, but according to their otherwise very informative page, ion thrusters have demonstrated fuel efficiencies of over 90 percent compared to chemical engines which are around 30% efficient. Dawn is the first long range spacecraft to use this technology, (some satellites use it to maintain orbit). It will remain in orbit around the rocky world for most of a year and then will continue on to study the slightly larger dwarf planet, Ceres.

Another view of Vesta from about 3,200 miles distant.