Short answers, pulled from the story.
The International Astronomical Union officially approved the name Rheasilvia on the 30th of September 2011. This approval occurred after NASA's Dawn spacecraft arrived at the asteroid Vesta in 2011.
The Rheasilvia crater spans roughly 505 kilometers across the surface of Vesta. This width equals 90% of the total diameter of the asteroid itself.
Spectroscopic analyses revealed distinct spectral signatures indicating olivine minerals exposed at the bottom of the depression. These signals suggest the impact penetrated deep through several layers of Vesta's crust and may have reached into the mantle region.
A series of troughs runs along the equatorial region of Vesta forming concentric rings around the main crater. The largest fracture system known as Divalia Fossae stretches approximately 1,500 kilometers long and spans about 200 kilometers wide.
Scientists propose that the event responsible for the Rheasilvia crater also generated HED meteorites found on Earth. If fragments ranging up to 10 kilometers in size survived bombardment until the present day, the crater must be no older than one billion years.