Via Sky & Telescope comes word that the Dawn probe has reached the asteroid Vesta, going into orbit around it last evening (PDT). Unlike the abrupt arrival burns of chemfuel rockets, Dawn's arrival was a gentle transition from solar orbit to circum-Vesta orbit - the first arrival burn by an electric-drive spacecraft.
The image, taken a week ago by one of Dawn's cameras, shows Vesta as a suitably transitional object, not quite spherical, but also not potato-shaped like smaller asteroids. According to the S&T news note, Vesta probably underwent partial internal melting during its formation, and so has a distinct core and mantle. One of Dawn's tasks is to measure Vesta's mass - implying that we don't actually know yet precisely when Dawn entered Vesta orbit, only that at some point during its gradual burn it must have done so.
Dawn will spend about a year orbiting Vesta before moving on to the asteroid belt's sole full-fledged 'dwarf planet,' Ceres.
This coming week we will return to the vexed issue of reaching Earth orbit. (Yes, last week slipped past me.) But for now, let this be a reminder that exploration of the Solar System is underway and continuing.
In other news, a belated note that I have added my Twitter feed to the right-hand column on the main page, below the archive links. But I haven't taken time yet to add the little bird logo.